Probably my most prized personal project, Calendar Countdown List Widget is a launcher widget that shows a countdown to user selected events from their device/account calendars.
I originally created this back in 2015 and have continued to work on it, with a big rewrite (2.0!) that I worked on while my 4 month old daughter naps.
The widget allows users to pick instance or recurring events manually, or automatically show countdowns to all events (with manual excludes). The widget supports color customization, and transparency.
Originally this was written backed by a content provider and some very overly complicated loader logic inside of a fragment. Version 2.0 has since been rewritten using Android Architecture Components: ViewModel, LiveData, Koin, and coroutines.