A popular (?) run-time library which was used to port many GNU and freeware UNIX programs to OS/2 text mode. The EMX environment must be downloaded separately, and could consist of everything from a single DLL (EMX.DLL) to a complete package with the gcc compiler to help users roll their own software.
Most GNU utilities, including make, sed and awk, are available as pre-compiled binaries. EMX is also documented with on-line help in the standard .INF hypertext format. As with many Unix bolt-on environments like Cygwin, most console apps compile without incident although there are some idiosyncrasies like problems with filenames with spaces in them and OS/2's distinct way of handling extended attributes (in C:\EA DATA. SF).
Sadly, I stopped using OS/2 before I knew what all these Unix thingies were, so I didn't play around with EMX's development side. For you daring never say die engineers who still use OS/2, you can find version 0.9d of EMX on the famous Hobbes OS/2 Archive at http://hobbes.nmsu.edu/cgi-bin/h-browse?sh=1&dir=//pub/os2/dev/emx/v0.9d.