You deposit, say one bitcoin with the server hosting the exchange, and then put in your bid or offer.
 When the bids and offers are matched and both parties agree the exchange begins directly between the clients multi crypto currency wallets but only one bitcoin (or equivalent in lite coins) at a time alternating between clients. After each one  bitcoin transaction in one direction is confirmed the equivalent litecoin transaction in the opposite direction is initiated. This is done automatically by the client wallets.
 If either client stops the transaction at any point the exchange holds the deposit to even things up if necessary.
 If you want to increase the increment of exchange you can put a higher deposit but apart from the deposits all currency exchange is directly between the clients.

 This is only suitable for crypto currencies not fiat.

 

Would it be possible to use a version of the bitcoin blockchain for decentralized web publishing. Rather than host my site on a server it would be broadcast on a 'webchain' and the publishers instead of paying hosting charges would provide pow to verify the webchain in a similar way to bitcoin miners. The published material and edits would be digitally signed. It would be decentralised and resistant to ddos and more difficult for any government to take down. Would this work?