Whatever it is, I've never seen it before and now I want to have my own just to play with.
These forums are running Discourse. It's a totally open source and free platform, so you can just launch a VPS on something like EC2 or Digital Ocean (my preference) and follow the documentation on setting it up.
I get the same feeling of this site as "Greenheart Games Forum" (The people who made Game Developer Tycoon). It's probably is the same platform
I already run a VPS setup over at QuickPacket, though I have heard good things about Digital Ocean as well.
This forums has that same feeling as I have felt in the River City Ransom Underground (Another Kickstarter project I backed on) forum, so I feel right at home.
Yeah, Discourse is awesome. I wish more forums used it. It's so fast and clean.
Yeah, I definitely prefer it over vBulletin and phpBB, which are what the vast majority of sites seem to still use in spite of them really showing their age.