Ask HN: State of Internet forums

I need a forum. I do not have much money to spend for this (personal thing; probably can do up to $49-59).

What is the stablest/greatest/latest thing out there with at least some plugins, and preferably a way to implement a single SSO system against an existing database with at least a few thousand users?

* I can't afford vBulletin, Xenforo, etc.

* Last I checked, phpBB no longer serves downloads temporarily due to some hack, or something, I don't know.

* SMF's community and ecosystem is kind of terrible.

* FluxBB is nice, but I'm waiting for the laravel release for integration, otherwise migrating will be another pain.

* PunBB is basically an abandoned FluxBB?

* NodeBB, FlaskBB seem really immature at this point, or at least not enough moderation tools or other management, and I am not comfortable enough in node.js to do manual editing.

* esoTalk is nice, but effectively stalled while waiting for Flarum.

* Discourse's resource usage is a bit on the high side, and I am not comfortable enough in rails/ruby to do manual editing.

* Why are the vast majority of forums in PHP?