I looked at Discourse, and for the scale of my projects the pricing is unmanageable. Hosted by them it's $1000+ a year; hosted by me it's still $100+ a year ($200+ for the first year). Installing it and running it myself requires spinning up a moderately high-end docker instance, which I'm unwilling to do (not only does it cost money, but I've only just managed to stop running my own servers, and it's great).