Been helping out a bit on Open Watcom Development and v2.0 is quite good now, it does have a few drawbacks but there being worked on.
For people working with Dos or Win9x support this compiler is allmost a must as its one of a few actively developed environments still supporting those architectures (djgpp being the other).
C++ support is still a bit flaky but its getting better by the day, however Open Watcoms STL does not yet support lazy instantiation so you need to have default constructible code atm.
WxWidgets 2.9 and greater does not build with Open Watcom because of this, 2.8 is fully supported though. The STL code is being worked on though so expect to see improvements over time.
Open Watcom now also sports a 64 bit to 32 bit crosscompiler so if youre on a 64 bit platform its encouraged to use the 64 bit version of the tools.
You can not make 64 bit code with it yet though (api only supports 32 bit or lower targets atm).
The C compiler is fully working though, and qbism has a version of his engine that works with Open Watcom.
Im MainTaining a version built with the intel compiler hosted on my Sourceforg site, it should be a little faster due to better optimization than the msvc built version.
I try to keep it up to date with current trunk, so it should be quite recent.
You can find those builds here