This looks like an impressive, feature-rich version of escape from the web (https://launchpad.net/eftw). Both use tornado on the backend and there seem to be some similarities in the multiplex classes. Escape from the web in turn shares code with ajaxterm.

Both (gateone and eftw) render terminal output on the server side using a python terminal emulator, while shellinabox mentioned in another comment uses a Javascript terminal emulator on the client side.

Edit: The docs say, the terminal class was written from scratch.