I too thought it was a variation of threadless.com, but it sounds like it's different... Though it still doesn't make much sense why they wouldn't let random people stumble into and join existing campaigns. A Kickstarter version of Threadless would be a very intesting thing to explore, especially if campaigns are allowed to last for a while (hint, hint).

I couldn't find it easily, either.

Featured and Exciting Campaigns were the only ones. Is there a complete list of active ones?

Hey guys - I replied above (http://news.ycombinator.com/item?id=5173296) but the short story is that until quite recently we didn't have enough traffic to really help organizers sell their tees, and didn't want to imply that we did by offering a marketplace.

We also didn't have a huge amount of cool campaigns at any one time (up until recently) - which would have made for a pretty poor browsing experience!

We're working on expanding our discovery tools, as wiwillia explained above, but any discovery tools will always be filtered, either manually, or by fairly stringent criteria, such as already having sold a number of shirts. As with any website that freely accepts user-submitted content, making it easily viewable to the public is inviting abusive and spammy submissions.