It's a forked version of MicroG Services to provide account support in Vanced and ReVanced apps.

microG Services is a FLOSS (Free/Libre Open Source Software) framework to allow applications designed for Google Play Services to run on systems, where Play Services is not available.
This fork tweaks MicroG to be usable by applications that require Google authentication such as Youtube Vanced.
Notable changes
● No longer a system app
● Package name changed from com.google.android.gms to app.revanced.android.gms to support installation alongside the official MicroG
● Removed unnecessary features:
Ads
Analytics
Car
Droidguard
Exposure-Notifications
Feedback
Firebase
Games
Maps
Recovery
Registering app permissions
SafetyNet
Self-Check
Search
TapAndPay
Wallet
Wear-Api