What category would it fall under to start (and competently market) a community website focused on some particularly relevant topic? I guess this is sort of alluded to in the How section, but let me expand on it a little.

One thing I've noticed is that there are some pretty slick CMS systems out there these days, for example BuddyPress which is layered on WordPress. It has a karma plugin for forum posts. I have been considering putting together a cryonics site from these components -- it almost seems decent enough to compete with lesswrong, but is much easier to set up than Reddit.

You could probably take just about any hobby/interest group and overlap it with rationality training. For example groups that develop plugins and themes for web sites could use rationality as both a brand and to help them do a better job.