EduNetworkBuilder is a simple program for teaching network principles.  It was inspired by watching a number of people struggling with PacketTracer in an attempt to undestand IP addresses, subnets, and gateways.  Most of their struggles were with understanding how to configure an IP on each device; they never got around to learning about how the subnets worked.
EduNetworkBuilder is geared to take all the complexity away, and let you visualize the network and packet flow in a very simple way.  It has proven itself already, as a great tool for teaching in lab-settings in Africa.
It is also set up to be a tool for self-teaching; If you can solve all the built-in puzzles, you should be well on your way to mastering networking.

EduNetworkBuilder is a Visual Studio program.  You should be able to download the current free edition of Visual Studio, open the project file, and make the project.  You should also be able to download pre-compiled versions from: http://tyounglightsys.ddns.info/EduNetworkBuilder