Arduino Real Time Clock library.
An RTC library with deep device support.
For bugs, make sure there isn't an active issue and then create one.
Installing This Library (prefered, you just want to use it)
Open the Library Manager and search for "Rtc by Makuna" and install
Installing This Library From GitHub (advanced, you want to contribute)
Create a directory in your Arduino\Library folder named "Rtc"
Clone (Git) this project into that folder.
It should now show up in the import list when you restart Arduino IDE.