Paint Roulette demonstrating HTML5 Canvas and WebSockets
showmetheco.de
Using the HTML5 Canvas element on the client side and Perl/Mojolicious (http://mojolicious.org) on the server side, both connected via WebSockets.
showmetheco.de
It also uses Canvas but doesn't need non-standard ports (this one needs another connection on port 843), allows semi-opaque colors, etc.
Apart from that: what does "clear" actually do? Does it clear the screen for everyone?