MyBB is by far the best free forum software, but it's seriously missing a few key features that would make it worth using over a paid solution.
I seriously hate the way MyBB devs approach the development, the software is still missing proper password security, Anti-Spam features, some decent SEO friendly url rewriting and a conversation like PM system and the devs are like "Hey, lets spend a year to integrate a twig template engine in 1.9!".
If they ever decide fix those (probably not in the next 2-5 years) i could consider it as a decent forum software, Untill then, IPB is the way to go.
