Unciv is a fully-fledged Civilization clone. It’s honestly insane that such a polished game is not only free, but also open source.

https://f-droid.org/en/packages/com.unciv.app/

OsmAnd~

Makes navigating around easier especially as someone who likes walking.

Edit because somebody mentioned about the lack of description and link of apps:

OsmAnd~ is a FOSS alternative to Google Maps and uses OpenStreetMap for its data. You can download it here.

Syncthing, which syncs my files between my phone and computer. I can rip a music CD on my computer and it’s instantly sent to my phone so I can listen to it on the bus or wherever.

There’s so many I could list, I’ll just mention 2 underrated ones I don’t see mentioned as much:

• LibreTube - Best YouTube client imo, has a very nice and modern interface, proxies videos through Piped for maximum privacy (No direct connections to Google are made), No ads/tracking, SponsorBlock + Return YouTube Dislikes, support for downloading videos, etc. It’s everything I’d want and more out of a YouTube client.

• URLCheck - Excellent app that allows you to preview what a URL is before you click it, includes tons of features such as scanning for malware, removing any tracking parameters, upgrading links from HTTP to HTTPS, etc. I can’t recommend this app enough for the security, privacy, and general peace of mind it gives you.