[notice]This software may not be legal to use in some countries or localities, or for certain uses.  We are not lawyers, so we cannot advise you on this.[/notice]

From the README.md file:

PURPOSE

If you’re using a VPN service today, you may have found the following limitations:

1) All or nothing. Either ALL traffic goes down the VPN or none – unable to be selective.
2) Only one VPN at a time. Cannot selectively route certain sites down one VPN, and others down another VPN.
3) Unless you’ve configured your VPN at the router level, it’s likely that only a single device can use your VPN at one time.

This project serves to address each of the above – see the FEATURES section.

Please review my blog post here http://darranboyd.wordpress.com/2013/07/05/selective-vpn-routing-solution-dsvr/

Note that this software runs on a Raspberry Pi. Full text and download links:
DSVR (Domain-Specific VPN Router) (GitHub)

If for some reason you don’t want to run this on a Raspberry Pi, but would instead prefer to do something similar using a DD-WRT based router, the same author covered that topic a couple of years ago:
StrongVPN PPTP on DD-WRT – Source based routing (improved) (Darran Boyd)