And it's debt based like real money:
Ripple is a Bitcoin like P2P system to track debt between parties. The debt is transferable so you can "trade your debt"!!!
You can also be you own Ben Bernanke by agreeing with a friend that you owe each other $100.000,000. This debt claim can then be Broken up in shares and sold like Ripple XRP is. Instant money out of thin air like a bank!
Well, Compared to banks however users can decide for themselves which debts they trust and which they don't.
Try not accepting USD from Goldman Sachs debts... with Ripple you could do that!
It is really not THAT hard to understand: Just as you get "IOUs" from MtGox when you deposit (they promise you to transfer you some USD or BTC in the future) you could also get IUOs from someone else. Once you realize that money (e.g. withdrawal request) then you erase the debt. Ripple just lets you trade this debt quicker and easier while still allowing anyone to redeem it. MtGox for example even issues these codes that let anyone redeem some value, Ripple is basically the same. You don't trade BTC there, you trade BTC redeemable on a certain gateway.