It works on MacOSX and Windows - and should work without too much modifications on Linux, I just can't be bothered...

The MacOSX version showcases some of the CanvasGadget limitation/bugs on this platform (mouse events not reported when outside the canvas, plus the returned character which is wrong, it's fixed well on Windows, and almost fixed on MacOS - though you can't write accentued characters on the MacOS version).
It's not really optimised as well, mouse selection might be slow when the window is maximised.
This aside, I tried to recreate some of the Excel behaviour, you can do multiple selections, cell editing (except on A1 which is a locked cell), basic copy and paste works with Control(Command) C/V, text formatting (fully working, though this example might show some unexpected results as I didn't took much time in doing it).
Tell me what you think of it!

Download (Mac) (zipped .app): http://www10.zippyshare.com/v/84742793/file.html

Download (Windows): http://www10.zippyshare.com/v/19500970/file.html