Every year, Stupor organises a Secret Santa event in the Audio Forum. Basically, you post in a thread saying what kind of music you want, and then, after a certain time period, each person is paired up with another person and has to make a song based on what this person asked for. Nobody knows who's making their present. On Christmas day, all the songs are shared with each other.
I had the pleasure of making a track for the user Nimble, someone whose melodic talent I really admire. I had a super tough time working on this because, and this comes as no surprise to whoever listens to my music, I usually throw a hell of a lot of instruments in my music. I basically stripped everything down to strings, piano, and the odd timpani/cymbal roll here and there, which really took me out of my comfort zone.