Conceived and created by the late-artist Peter Schmidt and "non-musician" Brian Eno, the first pack of creativity block-smashers Oblique Strategies (or Over One Hundred Worthwhile Dilemmas) was first published in 1975 and quickly became legend ...and went out-of-print even faster.
A description, from the set:
These cards evolved from seperate observations of the principles underlying what we were doing. Sometimes they were recognized in retrospect (intellect catching up with intuition), sometimes they were identified as they were happening, sometimes they were formulated.
They can be used as a pack (a set of possibilities being continuously reviewed in the mind) or by drawing a single card from the shuffled pack when a dilemma occurs in a working situation. In this case the card is trusted even if its appropriateness is quite unclear. They are not final, as new ideas will present themselves, and others will become self-evident.