KaSE

From the publisher (Red Anvil Publications):

KaSE is a situational attribute based system that uses a d20.  All events are judged on a single d20 role based on the appropriate attribute.

KaSE uses five attributes (Physical, Mental, Emotional, Social, and Spiritual) based on a regular scale of 1-4.  That number is altered based on situational modifiers and then squared.  Results against the environment (such as tests of skill) are rolled against the most appropriate difficulty on the master chart.  Results against other people are judged on a simple comparison based on which person gets the higher result.