From the tractorgen README:

Generates ASCII tractors.

This program generates ASCII tractors using the universal tractor
coefficient (TC). The intended audience is practical ASCII tractor
theorists and lay people interested in abstract tractor theory.

Before using this program, ensure that you understand the fundamental
theorem of ASCII tractor mechanics:

        "ASCII Tractors must have at least four wheels." [1]

WWW: http://www.vergenet.net/~conrad/software/tractorgen/