From the projects homepage, “A free-as-in-freedom re-implementation of Google’s proprietary Android user space apps and libraries.”
You’ll need a ROM with signature spoofing enabled natively or using a patcher like nanodroid-patcher. Magisk is optional but will help pass safetynet. Installation using nanodroid and Magisk is fairly easy.
This is app implements play services and location services. The location services piece allows you to choose your location provider with options to use local or online databases. This saves you from sending your location to google several times a day when NOT using GPS and more when you are. I didn’t run many apps from the google store but in general had few issues even with apps that were supposed to use google services. Although, one app I needed could not get location and the log showed the same error as a bug report from over a year ago.
This worked well when setup correctly but required that apps be installed after microg or the apps wouldn’t register correctly. GCM still sends data to google as an intermediary, the code running on your device is FOSS to limit your exposure to google. Some apps will probably miss funcationality since all of the messaging apis aren’t implemented. There’s no database telling you what will or won’t work, you have to find out for yourself.
This is a service provided by google to check that your phone has not been modified or applications won’t allow you to use them. Passing safetynet is a constant cat and mouse game with google changing setting so one day you’ll pass and then you won’t. Magisk should help by hiding your modifications but issues still seem to crop up based on the open issues.
Long Term Update
After a year plus of usage, I had a generally positive experience but, had to switch back after needing to use an unsupported app and unifiedNlp stopped working correctly.
A much needed app to put google at arms length on your phone. Usage is not for the faint of heart. You’ll want to limit your apps that use google services for the best experience. You’ll also have to be a part time sys admin with backups and updates of the device for when somethings goes wrong.