iVPN is a GUI for Mac OS X's built-in PPTP and L2TP VPN servers. This VPN server is usually only available on Mac OS X Server and configured through the Server Admin application. iVPN makes it possible to use the same server utility on the client version of Mac OS X.
All you have to do to set it up is to enter the user name and password that you want your VPN clients to use, the IP address range you want to give to your clients and then click start server. iVPN will handle all the other settings and start the VPN server.