Improv Games
Over the years, Improv groups have developed large collections of games and forms. In typical improv fashion, they are freely published for you to inspect, adapt and explore
The following sites can get your started:
Watch Tim Brown talk about the powerful link between Creativity and Play
Recommended Books about Games in Improv!
These two books present a great collection of improv games together with the theory and application.
Impro for Storytellers by Keith Johnstone
The Improv Handbook: The Ultimate Guide to Improvising in Comedy, Theatre, and Beyond by Tom Salinsky and Deboarah Francis-White.