Terrarium was created by members of the .NET Framework team in the .NET Framework 1.0 timeframe and was used initially as an internal test application.
As quoted from the website, the Windows SDK team evolved the game in the .NET Framework 2.0 timeframe two years ago. The source code for Terrarium doesn’t use the very latest .NET technologies. The source code is now made available so that you are free to modify it and adapt it to the latest .NET technologies.
In Terrarium, you can create herbivores, carnivores, or plants and then introduce them into a peer-to-peer, networked ecosystem where they complete for survival. Terrarium demonstrates some of the features of the .NET Framework, including Windows Forms integration with DirectX®; XML Web services; support for peer-to-peer networking; support for multiple programming languages; the capability to update smart client, or Windows-based, applications via a remote Web server; and the evidence-based and code access security infrastructure.