hopefully will support image preview, and I've got an idea on how to support saving files to disk, but I'm not sure if it will work it definitely won't work.
I developed it using IE 6 and Firefox 1.0.7, both for Windows. I'd be absolutely shocked if it works in any other browser, but even so, if it doesn't work in your browser, let me know your browser version and OS.
Using it is pretty simple, select foreground and background colors with left and right click, respectively, and left or right click to set pixels to the canvas.
Update: Now saves in Mozilla.
PS: only look at the source if you want to go blind.