Pianist Scott Hughes recently crowd funded (Kickstarter) a project to build a card game to help musicians practice improvisation. It’s called Tonic, and you can download it for free. Scott says:
I believe improvisation is the #1 greatest thing a musician can do to improve him or herself as a player and as a person. The tragedy is that it’s not taught in standard music programs, and as a result most musicians are afraid of it. I studied music at UArts and Temple and saw a lot of the usual problems, so I want to provide an alternative.