Freedom League: The Bronze Age
Whenever a one is rolled it is considered a Critical Failure automatically. If the check would have resulted in a success otherwise, the roll represents an unforseen accident. If the roll would have been a failure, then it represents the characters incompetence. If the character is an NPC, then the player whose character the NPC opposed may narrate the nature of the the Failure. If the character is a PC, then the GM may narrate the failure.
Whenever a 20, is rolled then the roll is considered a critical success automatically. If the check would have succeeded otherwise, this roll represents exceptional skill. If the character is an NPC then the GM narrates the nature of the success. If the character os a PC and the roll represents skill, then the player running the character narrates the nature of his success, otherwise the accident is narrated by the GM.
In combat, Critical Rolls have additional effects.