To actually get to the site you need to go to http://www.koding.com, there didn't seem to be any link in the docs.

The fact they publicly say its free does not strike me as a strength, how are they going to pay the bills to store all of my data?

It looks like it started life as an online php editor (kodingen.com) but now has broadened out to supporting vms with 'social' stuff.

Some of the main competitors are: - https://c9.io/ - http://compilr.com - https://codenvy.com

The general experience after playing with it for a few minutes is quite nice, robust file tree, good editor (ace), interesting news feed.