iVPN is an app that allows you to configure a VPN server. Mac OS X comes with a built-in VPN server and there are ways to set it up without iVPN, but they are a pain in the neck. iVPN provides a great graphical user interface that makes it easy for anyone to set up and run a VPN server on their Mac. Users of the server version of OS X should not install this app, because it will mess things up for them.
The graphical user interface allows you to set up users and security settings. There are two protocols supported: PPTP and L2TP. Both of them work fine and I have tested them in the past.
Configuring iVPN couldn't really be any simpler. All you have to do is create a user, set a password and tell the application what range of IP addresses to make available to users that connect to your Mac via VPN. You can even manually set your DNS addresses so that the users will use those by default.
You can configure iVPN to start when your Mac boots up for a true VPN solution. I have used iVPN in the past when I was away from home and wanted a layer of security to protect me when I connected to the Internet from public hotspots. It saves me some money because I don't have to pay a provider for it. My Mac tends to be stable and it can keep a connection indefinitely (most days anyway), so pairing it with iVPN is a win-win for me.