The Johari Window was invented by Joseph Luft and Harrington Ingham in the 1950s as a model for mapping personality awareness. By describing yourself from a fixed list of adjectives, then asking your friends and colleagues to describe you from the same list, a grid of overlap and difference can be built up.

View my Johari Window here.

(thanks to Jamey for the link!)

Further reading:
Wiki on Johari Window.
Neogenesis: Johari Window theory.