[rmidthun]

FATE. Designed to be about the simplest thing that could be called a system, but endless flexibility in what you use it for. The Accelerated version is about 40 pages, the Core version is a more detailed, but still less than the typical RPG rules set.

The system is designed so that the players can influence the events of the game at the cost of increasing difficultly. For instance, every character has a High Concept, such as "Best swordsman in the kingdom". This can be used by the player in many ways, such as celebrity notice, justifying related skills, background, etc. but the game master can also invoke it for things like bitter rivalry, getting conscripted or not being able to go incognito.

As such, the system can work at many different levels. One popular setting has characters as magical cats, another as post-human cyborgs. And it all works.

For a list of various settings: https://www.evilhat.com/home/fate-worlds-and-adventures/