I think they're still working out the kinks [1], but nevertheless, great when it works. No more 'behind' hosted demos for open-source apps, just let them instantly deploy it and play with it on their own.

[1] Tried the sample node.js app immediately, although I am getting "Deployed to heroku", viewing it throws a "No such app" - https://www.dropbox.com/s/bsl55sia46ymrwv/Screenshot%202014-...