Steve Crocker who originally worked on the ARPAnet protocols, is now leading a D.C. research firm developing a secure p2p software. What makes this so interesting is that the software is a lot like Aimster was back in the day, only Shinkuro is much more advanced. The great thing about Shinkuro is that all traffic is encrypted. 256 bit AES and 2048 bit RSA keys. Each Shinkuro message is encrypted with a unique key, and the key is transmitted under the RSA key.
Once the program is installed, you create a group and designate a folder to share with the group, you can also chat with group members using Shinkuro
Shinkuro offers secure messaging and secure screen sharing no matter what the OS. The software is as cross-platform compatible; Windows, Mac, Linux, and FreeBSD.
Windows screenshots: http://www.shinkuro.com/PCScreenShot.png