[append]
Found it. I think. Looks different than what I remembered, but, eh... it's called the "Ultimate Pen": http://www.snowmintcs.com/products/ultimatepenmac/
Wait... no, the one I used to have is called Desktastic: http://www.panic.com/desktastic/
Yep, that's the one. Although Ultimate Pen isn't too bad either...
Yep, definitely Desktastic. Still had a random list of binary from a while back. Eh, but Ultimate Pen is better, I think. Desktastic keeps me from reaching the desktop while it's open (I think..), has limited colors, and doesn't seem to support pen pressure all that well...
[keywords for google searches... Float, desktop, draw, sketch, macosx]