TL3 is a compact lisp interpretor that is an ancestor of Lush. Its copyright belongs to both me and Neuristique. It was initially used in the SN Learning System Development Tool. It was eventually agreed to release TL3 under the GNU General Public License. The lisp language is pretty clean with a full online documentation and a graphic toolkit. There is also a well documented extension mechanism for adding new primitives.
There is a unix version and a windows version.