People who have already played it can ignore this belated news message.
The Evasion is a small 6-level singleplayer modification for Half-Life. Set shortly after the devastating ending of Opposing Force you once again take control of Adrian Shephard while trying to figure out a way to get back to Earth.
Note that Opposing Force is not required for you to play it and as such Half-Life is the only thing you need to run it.