Retro Ski Run was written in Pascal code using Lazarus and Free Pascal Compiler - both open-source projects freely available on the web. It is published under a Creative Commons licence, which means both the software and the source code is freely available on request.
The author spent many months travelling to Europe and the USA to carefully survey the premier ski resorts featured in Retro Ski Run. I'm sure you will agree that you have to blink twice just to assure yourself you aren't actually there when playing!
Wiki: GettingStarted
Wiki: ManagingHighScores
Wiki: ManagingReplays
Retro Ski Run