Pixley is a strict subset of R5RS Scheme (or, if you prefer, R4RS Scheme), supporting four datatypes (boolean, cons cell, function, and symbol) and a dozen built-in symbols. The reference implementation of Pixley is written in 124 lines of Pixley (or, if you prefer, 124 lines of Scheme; and if you prefer more Scheme-ly metrics, it consists of 413 instances of 54 unique symbols in 684 cons cells.)
Except where noted as being in the public domain, the source code files in the Pixley project are distributed under a BSD license.
The latest released version of the Pixley language is 2.0. For more information on the language, reference implementation, and project, please refer to The Pixley Programming Language document.
Pixley development is hosted on Bitbucket.
There is also a git mirror of the repository on Github.