Matnet shows you how jiujitsu positions are all connected. Over 50 positions (including original artwork) have been mapped out to show you how to get from position to submission. If you're a complete beginner looking for an understanding of the big picture, this can help you see what's possible. If you've been doing jiujitsu for awhile and feel like you might have a few holes in your game, this can help you plug those holes.
The dream is to some day have every jiujitsu position that you can think of mapped out in this way, but the only way to get there is with lots of feedback. Check it out and see if there's anything missing--new positions and artwork are added all the time!