Best open source pptp option I am aware of. pptp doesn't give the best encryption in terms of VPN options, but it is the most widely supported by different clients. If you have to support a diverse set of users, it's the way to go, at least as an option for some.
very good project
Using it with RHEL5.5. Very simple to set-up. Very efficient too. I wonder why it is not included in RHEL distribution ?
Cost effective and robust VPN solution.