I've developed a huge interest in forum scripts since around October 2010 - when I set up the first iteration of what became EnigmaBoard on a hosted forum solution running phpBB2 (gross), which made me look into hosting stuff myself.
Since then, I've kept track of multiple scripts over time, trying to find that one single gem that did everything in an awesome and modern way. The only ones I found that didn't have the classic "flat" category>forum>threadlist design were Vanilla, whose people in charge seem to want to keep most of the new features on their paid hosting platform, and esoTalk, which is pretty damn awesome but development is slow, as it's run by one guy.
Discourse is a new open-source Ruby on Rails forum script with a focus on being very_modern_ (general descriptive term for omg this is different and looks newer than the stuff we had) and aims to be the next widely-used forum script for the next 10 years or so they say.
That's cool in itself, but Discourse is actually functional and works pretty well from what I've tried on the official Discourse forums and their sandbox testing forum, unlike some concepts I've seen. And they've already netted some big partners too, to provide discussion forums for and promote Discourse by extension, like How-to Geek and BoingBoing.
I'm really excited for the team to release the first self-hosted version (which right now, you can sort-of get off of their GitHub) and then a database converter so I can experiment with moving my various forums to Discourse.