传送门：进化/Portal: Revolution

Portal: Revolution is a fan-made mod for Portal 2 which plays before the events of Portal 2 in the dead and decaying Aperture facility.

Over 40 new puzzles

The campaign contains 40 brand new puzzles making use of new test elements and presents existing mechanics in a new way not seen in Portal 2.

Difficulty

Portal: Revolutions puzzle difficulty starts where Portal 2 stops, but fear not. All new mechanics and advanced portal tricks are taught to you. We have ensured through rigorous playtesting that every player can solve the puzzles. Although very few chambers require portals to be fired mid-air, no puzzles require advanced tricky movement.

Depending on your experience with Portal 2 mechanics, you can expect about 5 to 8 hours of playtime.

Set inbetween Portal and Portal 2, Portal: Revolution tells a brand new story using new characters. You play as a test subject who is awoken by a personality sphere called Stirling and join his mission to find a powerful device capable of restoring Aperture to its former glory.

ENGINE

Portal: Revolution uses a modified version of Portal 2: Community Edition's engine, which is a custom version of the Counter-Strike: Global Offensive

This allowed us to introduce many mechanics and improvements to the engine to create an experience which would be impossible in Portal 2.