I've exchanged a few messages with a mathematician before. We did a small project together, but then contact was lost.. probably due to circumstances on their side. I miss them.

Other than that, I've contributed a few bug fixes to projects from people I met through various posts. The collaboration periods were about two weeks and a month, maybe? Most of them were good people, but we mostly only talked about technical stuff. Whether it was because of my programming skills or something else, the connections never really lasted long.