Source
Well basically someone wrote a python script which basically allows the Blender Game Engine to recreate the famous portals from the game Portal
I've tried the demo scene and I've had quite a lot of fun! I might try and build a very simple level for it if I have time.
I took a screenshot of my blender session from a different camera angle than the one found in the BlenderArtists.org thread

(Click, and pay attention to the blue box portals)
Thoughts?
