Jailbreak without PC
There are two methods to jailbreak. These are Computer support jailbreak tool and Online jailbreak tool. Online jailbreak is the most comfortable method and no need for Computer support to it. Anzhuang/zjailbreak is the most popular online jailbreak tool for latest ios versions. Read more about  Without PC jailbreak.
zJailbreak
zJailbreak is the third party app installer method for latest iOS versions and iOS devices. zJailbreak initially released for iOS 9.3.5, and since then the zJailbreak team is continuously updating the compatibility against every iOS versions update. You can install unlimited apps and tweaks after install zJailbreak.

Cydia

Keen Jailbreak

Xabsi
Xabsi is alternative app stores for both Cydia and Apple App store. You can jailbreak apps using Xabsi for latest iOS versions and devices even you can install Cydia. There are app categories such as App Stores, Jailbreak, Customization, Game Stores, System apps.


Keen Team recently demonstrated about iOS 12 Jailbreak at at RECon conference. Previously they have showcased iOS 11.3.1 Jailbreak at Infiltrate Conference and iOS 11.1.1 Jailbreak using iPhone X at PoC 2017. As well as they proved the jailbreak possibility using iOS 11 and iOS 10.3.2 versions at MOSEC 2017.
Xabsi is alternative
Jailbreak without PC
zJailbreak
Keen Jailbreak
Cydia is the most popular 3rd party application manager for iPhones or iPads.
You must have installed the Cydia to install themes, system tweaks, widgets and many more.
Jailbreak (untethered, semi-untethered, partial or alternative) is the only way to download cydia for free to your iOS device.
We have listed all the Jailbreaking / Cydia installation methods for all the iOS versions.
Check your iOS version first. Then you can use following methods for Cydia.
Cydia for iOS 12 (beta) - Anzhuang Jailbreak app installer is the only method to install Cydia iOS 12. All features are not available with Anzhuang Cydia. It is available online Cydia IPA under the Velonzy jailbreak app installer to install Cydia online for iOS 12.
Refer - Jailbreak iOS 12 (beta)
Cydia for iOS 11.4.1 / iOS 11.4 - It has no any real jailbreak tool to download and install Cydia for iOS 11.4.1 beta and iOS 11.4.
But, it is available few trusted jailbreak solutions to install a special version of Cydia. Anzhuang & Velonzy works as real jailbreak solution. However, some functions may not work with this Cydia app.
Refer - Jailbreak iOS 11.4.1
Jailbreak iOS 11.4
Cydia for iOS 11.3.1 / iOS 11.3 - It has Electra Jailbreak as semi-untethered jailbreak method to get Cydia for these versions.
Also, Anzhuang & Velonzy are available online Cydia installation IPAs to install limited functional Cydia for these versions. 
Refer - Jailbreak iOS 11.3.1
Jailbreak iOS 11.3
Cydia for iOS 11.2 to iOS 11.2.6 - Electra Jailbreak available for iOS 11.2 to iOS iOS 11.2.6 versions.Yalong semi untethered jailbreak tool installs Cydia for iOS 11.2.6 / iOS 11.2.5 versions. Yalong jailbreak process can be completed through the Cydia Impactor.
Anzhuang and Velonzy are other jailbreak solutions to install Cydia for iOS 11.2 to iOS 11.2.6 versions.
Refer - Jailbreak iOS 11.2.6 / iOS 11.2.5
Jailbreak iOS 11.2.2 / iOS 11.2.1 / iOS 11.2
Cydia for iOS 11.1 / iOS 11.1.2 - It is available semi-untethered jailbreak method as Electra & LiberiOS for these versions to Cydia download free. However, all the Cydia features not possible with this time because Cydia iOS 11 update is pending by Saurik.
Anzhuang and Velonzy app installers install Cydia online to your iPhones & iPads as an app. Most of system functions are not work with Anzhuang Cydia and Velonzy Cydia.
Refer - Jailbreak iOS 11.1 / iOS 11.1.2
Cydia for iOS 11 & higher - Electra & LiberiOS jailbreak tools are available to jailbreak iOS 11 & higher versions too. These tools complete the jailbreak process using Cydia Impactor.
In addition to above, Anzhuang and Velonzy online app installers are available to install Cydia for iOS 11 & higher versions. 
Refer - Jailbreak iOS 11 & higher

Online Cydia Installers

When considering latest jailbreak tools, it has inability to work with Cydia. Saurik has not upgraded Cydia for iOS 11 & higher versions yet. Therefore it can be recommended to use alternative jailbreak solutions for latest versions to install Cydia.
It has few trusted online Cydia installers for iPhones and iPads. Anzhuang and Velonzy are the best online app installers. It uses jailbreak without PC method to install special version of Cydia.

Anzhuang

Anzhuang is one of the famous app installers in the world. It installs only Cydia configuration profile online and you cannot install Cydia store. Anzhuang uses Dev code extraction method to install jailbreak apps including Cydia.

Velonzy

Velonzy uses UDID registration method to install Cydia online on your iPhone or iPad. However, Velonzy Cydia not full functional.

Fake Cydia Installers

There are more fake Cydia installers available. Jailbreak is the only process which offers Cydia download free. Otherwise you may use alternative jailbreak methods for real Cydia. If someone asks to follow the different method to install Cydia, it is a fake or scam.
Most of sites asks to install two useless apps and run it for few seconds to complete the Cydia installation. But, it completely survey scam site. Make sure to avoid those scam sites.
pangulive.com
ricojb.com
saigonjb.com
This site ask to download 2 useless apps and follow the instructions. Pangulive.com site shows they can jailbreak iOS 7.0 to iOS 11.3 versions using two app installation method. Completely fake site.
Ask to install one game / vpn app as Cydia AppBundle to install Cydia. Completely survey scam site.
This site ask to install game / proxy free one app to get the device ID & complete the jailbreak. Another fake site.

Cydia IPA

Cydia is not available as an IPA. You cannot download it from App Store or any website directly, Most of Jailbreak app installers install Cydia automatically after the Jailbreak process.

Also you can use some Jailbreak app installers (Anzhuang, Velonzy) to install Cydia with limited features.
You cannot install Cydia without Jailbreak or Jailbreaking alternative method.

Download Cydia from 3rd party App Store

You can download the special Cydia version from some 3rd party app stores. zJailbreak is the popular third party app store. Other than that, Xabsi and iExtras app stores are ready to download Cydia. All of these app stores allow to instal Cydia as configuration profile. However, you cannot download most wanted Cydia features from this Cydia.

cydia.com

Jay Freeman (saurik) is the developer of Cydia. He is an American businessman and software engineer.  cydia.com is the official Cydia site. He created Cydia & related jailbroken softwares to customize the iOS devices. Cydia package manager initially released February 2008.
cydia.com
Saurik has completed more projects except Cydia. Anakrino, Cycorder, Cycript, Cyrket, Telesphoreo, Quotes and ircWAB are some of them.
Cydia Substrate
Other than the Cydia, Saurik has launched many tools. Cydia Substrate is another valuable project from Saurik. It can be used to develop third party addons for iOS and Android. When it occurs boot trouble, it can be forced to go safe mode using Cydia Substrate.  
Cydia Impactor
Cydia Impactor is graphical user interface (GUI) builder to arrange graphical control elements using drag and drop editor. This tool is very useful to install IPA files on iOS versions and APK files on Android. Most important thing is latest Cydia impactor tool is available for Windows, Mac or Linux OSs.

Cydia Extender

Most of people asks, what is the Cydia Extender? It is a part of the latest Cydia Impactor release. It is a tool which allow to browse, install and resign application without a computer. However it ask paid developer account to work. Otherwise you cannot install the Extender.

Cydia Eraser

Cydia Eraser is a tool and It helps to revert iOS version by removing all the changes which you made with Cydia. Cydia Eraser remove the jailbreak completely from your iDevice by clearing all the jailbreak apps, files.

Cydia Alternatives

zJailbreak
zJailbreak is the best alternative for Cydia. It consists of many jailbreak tweaks, Themes, hacked games, apps and many more as same as Cydia app store. Also you an install other Cydia alternative such as tweakbox, ZESTIA through zJailbreak. It is compatible with all latest iOS versions. Now, zJailbreak has installed over 5 million users.
ZESTIA
Zestia is another popular Cydia alternative by Leon M'laiel. It was earlier known as X-cydia. Zestia will let you install jailbreak tweaks on your device and offers a list of exclusive premium apps that you will never find in the Apps store. 
Tweakbox
Tweak Box is alternative for Cydia store which is specially designed for iOS platforms. It is an app store and a tweak installer for iOS devices. Tweakbox has Tweaked Apps, Flash Apps, modified games as well as you can install Apple app store paid and premium apps and games for free.
iNoCydia
iNoCydia is another popular web-based alternative for Cydia store. It consists of same Cydia features. It is compatible with older version of iOS 7 up to iOS 10 and took very long time to update it to support latest iOS 11. You can install Jailbreak tweaks from iNoCydia.
vShare SE / vShare VIP
vShare is alternative to the Cydia app store. It installs cracked apps on iOS devices from outside of the Apple App Store. vShare SE offers free premium apps. vShare VIP offers duplicate apps feature and it costs $10 subscription for annually.

Cydia Sources / Repos

Once you got the Cydia you need to add Sources / repos to it. Most applications are available through Community Sources and some sources you need to add manually. Cydia sources / repositories allow to search and download the Cydia applications to iPhones, iPod, and iPads.
Here is the list of Best Cydia Sources & Repos 2018.
BigBoss Repo -The Biggest and Most used repository 2018. It has thousands of tweaks, mods, apps and themes.
Repo link : http://apt.thebigboss.org/repofiles/cydia/
Modmyi - Modmyi is must have repository which is consists of many themes, apps, and games.

Repo link : apt.modmyi.com
SiNfuL iPhone - SinFuL is the best cracked Cydia Source 2018. It provides the free version of paid applications and many features.
Repo link : http://sinfuliphonerepo.com
App Cake - App Cake is another best Cydia repo 2018 which is consists tons of free games for your iOS device.
Repo link : cydia.iphonecake.com
Insanelyi - This is another best Cydia source with thousands of applications for download. You can find their latest updates and the newest application releases through the active forum.

Repo link: https://insanelyi.com

Cydia Tweaks

There are many Cydia Tweaks available in Cydia app store. Following Cydia tweaks are the most necessary tweaks among these.
O MusicDockX
O HideLabels10
O BioProtect X
O Double Tap Lock
O Sneaky Cam
O Activator
O Auxo 3
O Alkaline
O Browser Changer
O Bytafont 3
How to get Cydia using Electra jailbreak?
You can download Cydia for iOS 11.1.2 to iOS 11 versions with Electra jailbreak. Use following Electra computer support guide to install Cydia.
 
Step 01 - Download the Electra.IPA from the following button and download Cydia impactor from above of this page
 
Electra button
Step 02 - Connect your device to the PC or Mac. Run the Cydia Impactor from your computer. Drag the downloaded Electra IPA into the Cydia impactor.
Cydia Impactor
Step 03 - It will require entering your Apple ID and password to sideload Electra.IPA to your device.
Step 04 - When sideloading process complete, you can find the Electra Jailbreak app on your device homescreen.
Step 05 - Verify the developer profile heading through the Settings --> General and Profile and Device management --> Trust.
Step 06 - Then run the Electra app on your device and Tap the Jailbreak button to begin the Jailbreak. 
Electra app
Step 07 - Once the jailbreak process complete, your device will reboot and Cydia appears on your device homescreen.
Cydia on your device homescreen
Note - You have to re-jailbreak the device after every reboot because this is a semi-tethered jailbreak. Also you can get Online Jailbreak guide from Electra Jailbreak page.

How to Install Cydia using Yalu102 jailbreak?

You can jailbreak iOS 10 to iOS 10.2 versions with Yalu102 jailbreak for free cydia download. Use following Yalu102 jailbreak guide.
Step 01 - Download Cydia impactor
Step 02 - Download Yalu102 tool from following download link.
Yalu102 link
Step 03 - Connect your device to PC and Open the Cydia impactor.
Step 04 - Drag and drop the Yalu IPA file into the Cydia impactor and provide the Apple ID and password.
Step 05 - It will begin to install Yalu 102 app on your Device. Once complete the process Yalu 102 app will be available on your device homescreen.
Step 06 - You need to verify the app after installation.

Go to Settings --- > General --- > Device Management --- > Trust.
Step 07 - Now open the Yalu102 app.
Step 08 - Click on “Go” button. It will take some time and wait until the process complete. Your device will be restarted automatically the during the jailbreak process.
Step 09 - Finally Cydia is available on your homescreen.

Upgrade Cydia

Cydia last updated version is 1.1.30 with full official support for iOS 10 jailbreak as well as support for 64-bit devices, on 15th Feb 2017.
Coolstar launched the initial release of Electra for iOS 11 - iOS 11.1.2 with the access to Cydia. However, cydia iOS 11 support update is still pending by Saurik.
When you run the Cydia first time or after a long time, you will get an "Essential upgrades" message. Essential upgrade needs to function Cydia repos properly. This process update the Cydia package itself to install new packages and apps.
Step 01 - Tap on “Upgrade Essential”
Essential upgrades Cydia
Step 02 - Confirm to start the download and install.
Step 03 - It will take few seconds to complete. Once done, tap on Close Window.
Note: It is recommended to reboot your device after you install necessary upgrades. You may have to repeat Step 1 to open Cydia again.
Most popular Cydia apps
iFile - It allows to create, delete, copy, paste, rename, change permissions, zip / unzip multiple files or directories and transfer files via Celeste, Bluetooth, or AirBlue Sharing.
AirBlue Sharing - Share Notes, Photos, Videos, Music, Contacts or Voice Memos with any iOS device.
iBlacklist - You can block and hide calls or messages from any numbers you hate.
Hands-free Control - Access the “Siri” without even touching your iOS Device with Hands-free Control.
Sara - Sara is an alternative to Siri for older iOS devices.
ProTube HD - This an alternative for iOS stock youtube app with Youtube features
Winterboard - WinterBoard is best Cydia themes collection.
Grooveshark - You can get phenomenal music streaming experience with Grooveshark.
RecognizeMe 2.0 - Face recognition app for your iOS device to use as a security solution.
PKGBackup - PKGBackup is a process of reinstalling all Cydia apps at once.
How to install Cydia on iDevice?
install Cydia on iDevice
You need to Jailbreak your device to install Cydia. Otherwise, you can use Jailbreak alternative method to Install Cydia on your iPhone. Follow Electra Guide to get an idea about how to install Cydia. Once you jailbreak with Electra, it will automatically Install Cydia. As well you can follow the Yalu 102 guide to see how to download Cydia.
 

Install Cydia using jailbreak app installers
jailbreak app installers
Anzhuang and Velonzy are the popular jailbreak app installers and it install Cydia for latest iOS versions. Both installers allow you to install Jailbreak apps on your device including Cydia. However, This Cydia is not fully functional.