If you run GNU/Linux, a BSD, or Solaris, you almost surely have (or can install) all the external software needed to use ePiX. For Mac OS X, you will need the Apple developer tools, and will want to install an X server and the fink package manager to build a featureful *nix environment. Users of other operating systems, most notably Windows, face a challenge in running ePiX, though not an insurmountable one. The author's (second-hand) Windows-specific knowledge is summarized below.
``Under the hood'', an input file is successively converted to eepic, dvi, PostScript, pdf or eps, and if desired, png or mng. ePiX comprises a compiled library written in C++, a C++ header file, and four shell scripts--epix, laps, elaps, and flix--that automate the various file format conversions. Each script is written in GNU bash. Consequently, there are two absolute necessities: a C++ compiler (preferably g++) and bash. The script epix uses only these programs. ePiX is primarily a pre-processor for LATEX, but does not absolutely require LATEX for normal use. However, without LATEX and Ghostscript (particularly dvips), you can't view or print epix's output files, nor can you run flix or elaps.
A text editor such as emacs or vim that facilitates formatting C code is extremely useful for writing input files. ePiX comes with an emacs mode, written by Jay Belanger, that allows you to write, compile, and view ePiX figures without leaving emacs.
In the presence of LATEX and Ghostscript, only a few standard utilities are needed to run ePiX's ``conversion to eps/pdf'' script elaps, namely grep, sed, epstopdf, and ps2epsi.
Finally, flix uses ImageMagick's convert utility to create png images, and to assemble pngs into animated mng files. The programs animate and display are useful for viewing flix output.
Aside from their reliance on specific programs, ePiX's shell scripts are written using Unix-style pathnames. Thus, the most straightforward way to use ePiX is to install a Unix-like environment.