My local hackerspace, and broadly the US and European hacker communities. This is mainly because information security is my primary focus, but I find myself happier interacting with hackers because in general they tend not only to be highly outcome-oriented (i.e., inherently consequentialist), but also pragmatic about it: as the saying goes, there's no arguing with a root shell. (Modulo bikeshedding, but this seems to be more of a failure mode of subgroups that don't strive to avoid that problem.) The hacker community is also where I learned to think of communities in terms of design patterns; it's one of the few groups I've encountered so far that puts effort into that sort of community self-evaluation. Mostly it helps me because it's a place where I feel welcome, where other people see value in the goals I want to achieve and are working toward compatible goals. I'd encourage any instrumental rationalist with an interest in software engineering, and especially security, to visit a hackerspace or attend a hacker conference.

Until recently I was also involved in the "liberation technology" activism community, but ultimately found it toxic and left. I'm still too close to that situation to evaluate it fairly, but a lot of the toxicity had to do with identity politics and status games getting in the way of accomplishing anything of lasting value. (I'm also dissatisfied with the degree to which activism in general fixates on removing existing structures rather than replacing them with better ones, but again, too close to evaluate fairly.)