(We will skip the Xanadu versions prior to 1979, which were more varied.  See Xanadu History.)

There were basically two different versions of the Xanadu code between 1981and 1992.  Designed principally by Roger Gregory and Mark Miller, they are deep and brilliant, but they had too many cooks, reached for bridges too far, and were far too clever about the wrong things.

This body of code may still become useful and is already being admired for its extraordinary designs.

This body of code is now under open source development at udanax.com under the direction of Roger Gregory.