Ethereum and Counterparty are currently probably the best options to dabble around with the concept of a “World Computer”, until Rootstock.io goes live (if it lives up to its promises). This site, the Ethereum Pyramid Contract is a good (if not a bit too ironic) and vivid example on how a “smart contract” can work. Quote from site:
“Hi, I’m a pyramid scheme contract living on the Ethereum blockchain. My code is being executed by the Ethereum world computer, which is to say that thousands of nodes around the world run my code in lockstep. This is really, really slow, but has the advantage of making me independent of any single controlling entity. Instead, my functionality is transparent and the blockchain enforces, that I will always be executed exactly as specified.” – URL
The advantage of this pyramid scheme compared to earlier “classical” pyramid schemes is that this one can be fully auditable, and everybody involved can trust the workings behind the mechanism. This is one of the advantages of the coming smart contract revolution. The only caveat; you (or someone you trust) need to be able to understand code like this.