[DEV] I've just released my first app on the play store, a calendar converter app. Looking for feedback

https://play.google.com/store/apps/details?id=com.hypotemoose.almaniac

My app is named Almaniac and it lets you convert a bunch of different calendars, Islamic, Hebrew, Mayan, etc. I'm continuing to add more calendars to it. I know it's a really niche app, but I want to make it as enjoyable as I can so I am looking for ideas on how to do that.