Tachyon is a parallel/multiprocessor ray tracing software. It is a parallel ray tracing library for use on distributed memory parallel computers, shared memory computers, and clusters of workstations. Tachyon implements rendering features such as ambient occlusion lighting, depth-of-field focal blur, shadows, reflections, and others. It was originally developed for the Intel iPSC/860 by John Stone for his M.S. thesis at University of Missouri-Rolla. Tachyon subsequently became a more functional and complete ray tracing engine, and it is now incorporated into a number of other open source software packages such as VMD, and SageMath. Tachyon is released under a permissive license (included in the tarball).