As part of the Potato Sack promotion last year a number of indie games received updates featuring content from Valve games. I didn’t take much notice of them at the time but I just found out that The Wonderful End of the World got a secret level with companion cubes! Love the cover of the similarly named Portal song!
Very cool use of one of my favourite songs.
It’s a great game too, but I haven’t unlocked the level required to play this one, at least on my desktop machine. Must check my laptop though!