GECO is a CLOS
-based library for writing Genetic Algorithms. It is a fairly flexible framework that can be used for experimentation and for the solution of a variety of problems. Documentation is available, and it includes two simple examples. It was written by George P.W. Williams, Jr., and it is distributed under the GPL.
Version 2.0 is part of the archives of the CMU AI repository. An updated version is hosted here.