Note that the program is only part of the Tex package. You need FONT METRIC files (TFM), style files etc. to have a working Tex system. TEX is copyrighted by Donald Knuth to prevent faulty programs calling themselves TEX. In order to be called TEX the program must pass the TRIP test supplied with stadand distribution. This port now passes TRIP. The UNIX TEX distribution is Public Domain software.
You also need a output device and driver to make TEX worthwhile. Access to a Laser printer with lots of memory is preferable. It is possible to print fair quality output on on dot matrix printer at 240 pixels/inch ( Epson compatibles). There is a public domain driver program to do this but it would be extremely slow ( 10 minutes/page). There is a nice public domain previewer DVIST which allows you to view the ouput on the screen before transferring to your favourite mainframe and laser printer.