As Felix mentioned, the company behind Discourse is a great address for Discourse hosting.
That’s still true, but they also offer a 50% discount on packages for registered non-profit organizations (see).
As Edgeryders, we don’t exactly offer Discourse hosting but sub-communities. Means, we don’t compete in the Discourse hosting market, we have a niche for people looking for a forum associated with an established online forum in the activism / grassroots innovation realm … plus getting the discussion analysis tools that we build around here. For the details, see here.