Left 4 Dead 2 F2P this weekend or US $1.99 to own.

Complete a campaign with a person who don't own the game on a free weekend, quite a rare achivement as last time it was free to play it was over 2 years ago.

Takes 2 seconds to google.

Possible way to obtain the "Good Guy Nick" achievement.
1) You need at least 2 players that obtained Left 4 Dead 2 during the free weekends:

(You can see the day you obtain the game on your purchase history.)

October 25 - 29 2012
July 4 - 8 2013

2) All the players must change their system time to one of those dates

• I belive hosting a local server is the best solution also, because players and server are gonna have the same date.

3) There should be no bots.