Freeform Role Playing System is a very lightweight game mechanic based on interpreting d% rolls without strict guidelines. The system is intended to support roleplaying in Tékumel.
From the introduction:
This gaming system is based on that described by Dr. Barker for his own gaming sessions (as described by Bob Alberti. The concept is to roll 1D100. The lower the roll, the better the outcome. For those desiring a little more detail, this system may be helpful. It is “fuzzy” and requires quick thinking and cooperation on the part of the referee and player(s).