Edit: apparently I do not recall correctly. I remember someone saying something about open source, and he posted something to github. I incorrectly linked the two. Thanks to those posted more accurate information below.
I'm not sure if "open sourced" is the right word(s) here. I can't find a license in the repository, so it is not released as open source and the code can't be used without breaching copyright.
Iirc it was mostly about storing some user preferences and providing push notifications.
Reddit apparently has no async API for notifications, so 3rd party apps are forced to regular polling.