OpenTransactions does that. The decentralized server side software completes the transactions you implement on your desktop software. Watch the videos for more information:
Wiki
http://opentransactions.org/wiki/index.php?title=About
Exchange demo video
https://drive.google.com/file/d/0B1elJotjR_t6OS1pV3duMEpWSGs/preview?pli=1
why is this not common
1. Still in development - just in beta
2. Adoption not realized. (Network not established)
3. Learning curve. (This new technology takes some reading to understand/comprehend)
4. Market is still maturing. Takes time for people to adapt.