This is an open source release of the Watcom C, C++, and Fortran compilers. Michal Necasek has an article describing how to set it up.
http://pages.prodigy.net/michaln/os2/Watcom11c.html
You can find the latest release here.
http://downloads.openwatcom.org/ftp/
Source: OS/2 Warp News and Rumors