microG GmsCore is a free software reimplementation of 
Google Play Services. It allows applications calling proprietary Google APIs to run on AOSP-based ROMs like 
LineageOS, acting as a free replacement for the non-free, proprietary Google Play Services (sometimes referred to as the more generic term "GApps"). It is a powerful tool to reclaim your privacy and freedom while enjoying 
Android core features (although apps you use that take advantage of it may still be using proprietary libraries to communicate with microG, just as they do when communicating with the actual Google Play Services).
Features
- Opt-in to Google Services and extend application support
- On-/Offline location service
- Easy on battery, memory and CPU
- No bloatware
- Works on real devices, test emulators and virtual mobile infrastructure
- Free (open source) (Apache 2.0 licensed)
For a full-working microG setup, you may consider to install a 
Google Play Store replacement application as well as the Services Framework Proxy (GsfProxy) module to provide Google's push messaging service.
Comments and Reviews
Still in development and incomplete, but clearly the hero we needed!
Great project, thank you
A great alternative to google services
It gives you the option to opt-out of google spyware and be reserve your privacy.
I'm so grateful for the developer. This is one of the most important software that humanity needs
I will continue donating to this project