Also, there is a browser version:

ASCIIpOrtal is by Joe Larson with sounds designed by Steve Fenton. Original concept inspired by Increpare’s Portile game, Super Serif Bros, and Valve’s Portal. Source code is included in the zip.

ASCIIpOrtal is a unique puzzle game. You can create custom maps so even when the game is over the fun doesn’t need to end. Use a text editor and share the maps you create on the ASCIIpOrtal forum.