I believe that it was always open-source.

I remember them promising to open-source it early on and then waiting at least a few months for the code. At the time I was jaded and thought they'd go back on the promise, but I'm grateful they didn't. It's the most polished FLOSS map app.

It wasn't always. It started as MapsWithMe by a swiss company, which gave it away for free with a pro version (for which I paid), then mail.ru took it over and made it opensource (while all my build attempts failed) and then a new owner later added tons of ads and stuff into it and made it closed. Then some people forked the slightly older open source version.

Those people are the original founders who took it open source, which was a great move since otherwise it'd have become just another piece of shovelware getting enshittified into oblivion.