This is very impressive. Kudos. It seems these days people can do anything in Javascript. I've never been a Mac guy but I recognize this as a classic program, presumably the inspiration for MS Paint on Windows which I have used a lot (for "programmer" graphics). Recently I bought a Mac with a view to maybe transitioning from Windows to Mac, like all the cool kids these days. I was rather surprised (horrified?) to find there is no standard simple Paint program shipped with the Mac these days (I don't think).
You're right, and I'm horrified, too. The various replacements are horrendously overcomplicated. Heck, I'd use this retro app as my go to drawing app, Chicago font and all, if it had a bigger canvas and the ability to save and read files.
I also have fond memories of MacPaint. Don't know when it was removed. Nowadays, when I need a quick paint program on a machine (Mac or PC), I use Sumopaint (
http://www.sumopaint.com/app/ ). It uses Flash and is pretty powerful, not simple but easy enough to use.