Wippien

Wippien is an Instant Messenger with VPN support that combines different protocols: ICQ, MSN, AIM, Yahoo, Google Talk. NAT traversal techniques are used to penetrate NAT devices and make direct connections between peers, and allows you to access your friend's resources (such as system shares, printers, etc.).

Wippien uses the XMPP/Jabber protocol to locate your friends and see their presence status, and after that it initiates direct peer-to-peer secured connections with them. Peers needn't know the real IP address of other peer - Wippien assigns a temporary one for the session lifetime. If your friends don't use Wippien, you can still use Wippien as an ordinary instant messenger.

You can download and use Wippien for free, both for personal and commercial usage. If you like Wippien, you can adjust or rebrand it to suit your needs. Source code is available and can be downloaded from the vendor's Web site. Wippien uses several 3rd party components which need to be licensed separately. Note that you still need to obtain licenses for those components if you plan to rebuild Wippien on your own.