Narbacular Drop

Narbacular Drop is puzzle video game developed by Nuclear Monkey Software, and is the spiritual predecessor to Portal.

Synopsis
A princess, called No-Knees due to her inability to jump, was admired by her entire kingdom. A demon, imagining her kidnap would help in his quest to conquer the world, captures No-Knees. He then lockes her inside a cage in his mountain lair, under patrol of his Impy minion. However, Wally, the spirit of the mountain, was mad at the Demon for creating his dungeon lair inside his home. He tells No-Knees he would assist her in escaping as long as she helped him to defeat the demon. To escape, Princess No-Knees is allowed to use Wally's magical power; she can look at any two flat surfaces and break reality, making an instant link between them using two portals. She'll then use this to travel through five different chambers all the way to the final boss.

Development
The game development had 4 "milestones": Pre-Alpha, Alpha, Beta, and Final.