Sileo is Cydia replacement Package Manager for Jailbroken iOS devices.
It s a multi-contribution project made by experienced developers.
There is no Cydia update from saurik for a long time. It is a long overdue Cydia update for iOS 11.X.X versions. Now it has arrived iOS 12.X.X too. I It seems saurik no longer being maintained Cydia.
However, this is compatible iOS 11 onwards and not compatible with a backward version such as iOS 10. 
Coolstar published a Youtube demonstration video about how is the Sileo user interface in action.
Version Compatibility :

iOS 12.1.1 , iOS 12.1 , iOS 12.0.1, iOS 12, iOS 11.4.1, iOS 11.4, iOS 11.3.1, iOS 11.3, iOS 11.2.6, iOS 11.2.5, iOS 11.2.2, iOS 11.2.1, iOS 11.2, iOS 11.1.2 , iOS 11.1.1, iOS 11.1, iOS 11.0.3, iOS 11.0.2, iOS 11.0.1, iOS 11
Device Compatibility :

iPhone X, iPhone 8/8 Plus, iPhone 7/7 Plus, iPhone SE, iPhone 6S/6S Plus, iPhone 6/6 Plus, iPhone 5S, iPad 5(2017), iPad Pro 12.9 (1st & 2nd generation), iPad Pro 9.7, iPad Pro, iPad Air 2, iPad Air,iPad Mini 4, iPad Mini 3, iPad Mini 2, iPod Touch 6

Sileo Release Date

The developers still not confirm the Sileo release date. Most probably Sileo will be bundled with the next versions of the Electra.
Sileo Features
Old packages and setup will stay when switching to Sileo
Sileo will compatible with every Cydia package and repo.
Cydia purchases can be accessible from Sileo.
Sileo not compatible with 32-bit devices.
Sileo not compatible with older versions such as iOS 10.X.
Here are some hints extract from the developers’ tweets about Sileo package manager.
Therefore Electra team has planned to release a user-friendly alternative package manager called as Sileo.  Jailbroken users can download new jailbreak tweaks, themes, and much more through Sileo. It is designed  for 64 bit command line tools + libraries.
Here are some important news about Sileo
Sileo Developers confirmed Dynastic Repo supports with Sileo.
Sileo Developers confirmed Dynastic Repo successfully works with Sileo Package manager. Some few awesome apps are able to install with Dynastic Repo. ShortLook, TranslucentMessages, Countdown, TranslucentWallet apps are few of them. AppleBetas (@AppleBetasDev) is the main developer and designer of the Dynastic Repo. nullpixel (@nullriver) and Eric Rabil (@ericrabil) are the developer of this repo.
Sileo Developers
Sileo built by Atom Development. Here are developers who contribute to the Sileo project.
Andy Wiiks :

Andrew Wiik/@Andywiik is iOS tweak/web developer. He is a student at the University of New Haven.

LittleX, Maize, True iRadio, WipeTracks, and Horseshoe are some of the tweaks developed by Andy.
Coolstar :

Coolstar is American windows/ iOS and jailbreak developer. He is the developer of Electra Jailbreak for iOS 11.3.1 to iOS 11 versions. ClassicSwitcher 3, 3D Switcher, Anemone, ClassicLockScreen and ClassicLockScreen are the iOS projects done by him.
LaughingQuoll :

Laughing is the Australian iOS tweak /app developer. Noctis, Scriblit, and Decorus are some great Cydia tweaks developed by him.
Alessandro Chiarlitti :

Alessandro Chiarlitti /@aesign is  italian UI designer and Coder. Electra toolkit designed by Alessandro Chiarlitti.
CoolStar has confirmed Sileo Support range as iOS 11 and Higher versions. iOS 10 and older version will not be supported with Sileo according to the CoolStar’s Twitter message.
CoolStar has announced Cydia replacement is coming soon.
One of the Sileo developers LaughingQuoll has hinted about Cydia replacement.
Coolstar tweeted a screenshot of Sileo on iOS 12 and Anemone.
According to the screenshot, seeing Anemone, he could be running a jailbreak on the iPad. Probably he is just testing the IPA. It might come with Sileo since Coolstar said it would be released soon.
Chiarlitti says Sileo is almost ready, Our developers just need to sort out a few things. Most probably it will release before the end of 2018.
Sileo coming soon according to developer recent tweet.