Under the Creative Commons BY-NC-SA 2.0 License, Chad of Aarchon has implemented a playable version of Cards Against Humanity using the Lua scripting language. Below are instructions for how the game is played, on Aarchon. The source code for our implementation is available here, and a table of the cards we are using is found here.

Cards Against Humanity is a game played by at least 3 players on Aarchon. In
this game each player will receive a hand of 10 white cards from the 
Gamemaster. Each turn a black card will be played which will have either a 
question or be fill in the blank. The player will then play one of his white 
cards to create an answer, or fill in the blank on the black card. The goal is to 
get other players to vote for your submission, by either being the funniest 
combination or some other metric. After all the cards have been played or too 
much time has elapsed the game will move on to the voting phase. A player may 
vote for any combination for any reason they choose, but may not vote for their
own card. The winner of the hand will be announced and they will receive 1 
point. When a player has reached 5 points the game will end with that person 
as the winner.
 
To start a game: send a tell to the Gamemaster with the phrase "start"
Example: > tell gamemaster start
 
To join a game that has been started: send a tell to the Gamemaster with the
phrase "join"
Example: > tell gamemaster join
 
To get receive help on the available commands: send a tell to the Gamemaster
with the phrase "help"
Example: > tell gamemaster help
 
To show your current hand: send a tell to the Gamemaster with the phrase "show"
Example: > tell gamemaster show
 
To display the current cards played: send a tell to the Gamemaster with the
phrase "display"
Example: > tell gamemaster display
 
To play a card: send a tell to Gamemaster with the phrase "play <#>" where
number is the card number given when a player's hand is displayed, or click
the link given if your client supports MXP.
Example: > tell gamemaster play 4
 
To vote on a card: send a tell to Gamemaster with the phrase "vote <#>" where
the number is the card number given when all cards have been played and 
displayed, or click the link given.
Example: > tell gamemaster vote 2