Tripwire details the origins
of Valve's crazy Portal 2 themed Potato Alternate Reality Game. It's an interesting read that explains what elements of the game worked and how they reacted with each update to try to guide players in the right direction.
At the end of the day, we had an incredible amount of fun both in the design and creation of the ARG and the content for Killing Floor. Valve, as always is an amazing partner to work with, allowing us full access to their IP. Working with all the other companies involved was also a great opportunity to make new friends in the industry as well as toss ideas and suggestions to each other on our current games and future projects perhaps. One theme I think many of us came away with was that collaborations are fun and the games industry needs more of them.
Towards the end of the article there is a hint
that there is more to come for Killing Floor. An announcement at the Red Orchestra: Heroes of Stalingrad Steam page confirms that and teases more to come for The Ball as well.