Sketchfu is an online software program tool that you can draw some cool stuff online and share it with other people, while it is almost Microsoft Paint basic, it does have a special use that I like about it, and that's to sketch quick random notes or ideas online and share them with people who care.
When I said basic, don't be put off by this, because there are some fantastic examples of Sketchfu and some of them are real masterpieces in their own right, take this Avatar sketchfu, which is just amazing, best to watch it at it's highest speed of 256. Sketchfu has certain given me a real interest in this program as before I'd orginally dismissed it as a basic Microsoft paint program, but what you can do is build up layers of colour to almost sculpt and build piece of artwork and that to me is truly amazing from a free program.
I highly recommend you check out this free drawing software tool, Sketchfu is amazing and while you are there, take a look at others art, it's excellent!
Go and do some Sketchfu