I am in America.

Meetup, library boards, etc. are useful, but I don't need more groups, I need to know which of my many choices are likely to be useful. I'd like to do better than showing up at vaguely interesting meetups and seeing if they happen to be comprised of interesting people... Although this basically is what I have been doing. It is not a motivating task.

Volunteering tends to be very good, except that there is usually (in my area) an oversupply of religious people at the non-political charities, and an oversupply of mindkilled people at the political ones. Still, a good suggestion, and I should probably focus on finding new opportunities of this sort.

I think these are good general suggestions that fit well into this thread, but they are not quite what I was looking for. However, the fact that you could provide a fairly comprehensive list that more or less matches my own does confirm that I am not missing any easy targets, and that is very useful information.