Open Watcom Compilers now also updated.
Changes:
A lot of stability issues fixed, and a few additions to the CRT (C++ still needs work but its slowly getting there, anyone with C++ knowledge concerning building a new STL from scratch are welcome to submit patches).
Open watcom while now able to operate with 64 bit logic still produces 32 bit executables so work on a 64 bit api would also be welcome.
Atm im trying to draft as many developers as possible to get this beautifull compiler up to speed, why you might ask

well for one windows 95 was built with the old watcom compiler and it still has some very nice
optimizations for DOS/OS2 programs but the windows part needs a lot of work and if you help you can one day boast that you helped making this

and it would also be a free community driven compiler who could rival the greatest free versions from MS and MinGW64 with better support for the windows platform as well as superb support for older OS like OS/2 and several free DOS clones.
Why not just stick with MinGW and offshots ? well to be frank as explained above this compiler actually kickstarted windows, it sports superior optimizations compared to a lot of even modern compilers but its also
a hard compiler to learn to control which is why many devs swear by it cause it forced them to actually learn how things work. Dont be afraid its not impossible to get this compiler to do what you want but it does
make things a little challenging. Needless to say there are many groups who can and will help you if you get stuck and jiri malak who maintains the source atm will help you as best he can or point you to members who can.
My build uses the intel compiler via msvc2013 which allows better optimization of the bootstrap compiler (saves a lot of time building this) but else its a pure openwatcom build.
If you need ms directx support you can pretty much replace the libraries and headers in h/nt/directx and lib386/nt/directx with the ones from whatever directx sdk you got from ms.
A few things are still a little dodgy like wxwidgets obcd32 support is broken same goes for a dynamically linked wxopengl library which fails with a linker error probably due to some more recent changes.
The thing is that openwatcom uses its own specialized calling convention __watcall which might need patching of some parts of a source to fix building it. Removal of this call would break openwatcoms auto optimization routines so its a between a rock and a hard place scenario. Besides that wxwidgets works fine with open watcom allthough the latest versions from 2.9.0 and up cannot be built with it due to changing more of the code to unsupported C++ routines. wxwidgets 2.8.12 builds just fine with it and the test prgrams work as a charm also.
curl also builds but i noticed i could not use ssl encryption due to some error. zlib ogg vorbis openal works just fine, as well as the png and jpeg libraries.
So all in all the C compiler seems to work for most purposes now the C++ compiler still needs a hand.
Productivity is a state of mind.