The site (awesomely) says that most of the code powering it is openly available on Github (https://github.com/ajaxorg/cloud9) - out of interest, which parts have you developed separately for your service?
Pretty cool, I have it running[1] on my box now, but I can't seem to figure out what the Run feature is supposed to..I'm guessing run the code in the second pane, but it's not clear with no docs...Also, is this designed to execute only for Javascript? Your site at http://c9.io is down and I don't see anything in Google cache so I can't read up there either.