OpenCanvas is a drawing software. Under my point of view, it's one of the best if you want to draw like you would with a pencil and a paper. It's not that powerful like photoshop or others, because they are focused to photography, retouching, etc. But if you like to draw with the computer, specially if you use a tablet, it's a good idea trying it. Wacom tablets at least work perfectly.
I love OpenCanvas a lot; however, I lack the tablet to really enjoy the drawing experience with. Sadly, a mouse doesn't really suffice when it comes to drawing something (even with the emulation of varying pressure with each mouse click - oekaki's so hard XD). I heard that OC was one of the best programs to use when it comes to working with tablets; I'll have to find myself a job sometime and buy both a tablet and the program to see how well it works for myself. X)
Don't know about OpenCanvas but you could try Project Dogwaffle. They have a free version and it is pretty powerful and fun.