See other forum post; someone's resurrected it at https://github.com/trackballs/trackballs/ and https://trackballs.github.io/.
There is a continuation of this project at https://github.com/trackballs/trackballs and https://trackballs.github.io/ , which has updated the code to be able to work with recent SDL, Guile, and OpenGL. From what I've seen, there has been minor levelset retouching, but no new levelsets as of writing :-(.