We present Pixley, a strict subset of R5RS Scheme. Pixley supports four datatypes (boolean, cons cell, function, and symbol) and a dozen built-in symbols. The Pixley reference interpreter is highly meta-circular, being written in 140 lines of Pixley (or, if you prefer, 140 lines of Scheme.)
Pixley is also (depending on how you count them) my 50th programming language (that I'll admit to!) This puts me squarely in the ballpark of Wouter and Aaron, and suggests that I plan to be personally responsible for a significant fraction of the next 700 programming languages.
Check it out at http://catseye.tc/projects/pixley/