...at a quick glance the github -project (https://github.com/projectM-visualizer/projectm) seems to be newer, but there's no mention of each other in either of the sites.

Hmm. I'm not sure what you mean by tagged releases, but there seems to be a branch called stable, which seems to be updated to only contain code deemed stable for releasing... effectively, a commit there would probably be a "release" then?