I think it's StreetComplete you're talking about. It's still working and is a great beginner-friendly app to get into mapping for OSM.

One of my favorite pictures on the internet.

What's that music player on the lower-left corner of the first screenshot?

Nice! Haven't heard of it, thanks.

>Developers when their girlfriend cheats on them (she's now free and open source)

The Nicotine+ client is FOSS, the Soulseek network is not though. Just a clarification. It's still the only relatively widely used means of obtaining music besides torrents, even though people can share any kind of files, not just audio ones.
With FOSS, self-hosted, Subsonic-compatible music media servers like Navidrome, one can build a streaming-site alternatuve with one's own collection.