Open Watcom could use someone with C++ knowledge to help finish there version of the C++ standards library.
Its about 50% done sadly the project lacks developers so it wont be finished any time soon unless someone chimes in 
 I have helped squash as many bugs as my limited understanding allowed me to, but i only recently started dabbling in C++ so i cannot help them in that regard. 
If anyone here can im sure they would appreciate the help though 

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As for benefits Open watcom is a multiplatform compiler that allows making programs for several operating systems on one platform (you can make Linux executables on say Windows and vice versa). 
OS support includes Linux / QNX / OS/2 / dos / Windows 9x - NT / AXP NT atm.
The C compiler is mostly complete and most of the bugs i helped squash was in the w32api. 
The C++ compiler is working but because the STL still needs a lot of Work not everything builds with it yet, i did manage to compile most of wxwidgets with it though so its atleast in a usable state.
If you want to help Development you can make commits to 
 
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