Over the new-year I wrote this little Free Software (LGPL) app for sketching stuff. It's called SketchThing.
With the impending proliferation of tablets and touchscreens my plan is to make a sketching app which runs on all kinds of tablet/touch friendly devices and browsers, online and offline, and will sync your sketches to whatever device you are using, wherever you are using it.
At the moment it's running on those Apple portable devices, since that's what I have access to thanks to my contract work for RjDj, and I'm quite glad that I have found a way to make Free Software which runs on those devices legally through the web app method. I hope to port it to at least Firefox, Android, and Chrome OS as well.
The core library, sketchthing.js, is device agnostic and should run on anything which supports HTML5, such as Firefox and Webkit. What the library does is take an arbitrary HTML element as an input, and then replace it's innerHTML with a canvas of the same size which can be sketched upon.