I've been geocaching for a couple of decades now, although very low-key. One reason has been that geocaching.com became such a pile of turd some time ago.

What other sites exist beside that one?

Personally I would be most interested in ones that have a reasonable amount of caches in Finland and Baltics, but maybe generating a somewhat comprehensible list of geocaching sites would be of use in general, so maybe let's try to collect one here?