Look into "open transactions" by fellow traveller;

https://github.com/FellowTraveler/Open-Transactions

https://en.bitcoin.it/wiki/Open_Transactions

http://vimeo.com/28141679

http://www.youtube.com/watch?v=HSgpStCTw2g

http://agoristradio.com/?tag=open-transactions

 I think it does what you are describing by matching orders, etc for any asset types.