Overview of EWin
EWin is a wrapper library for Windows programming. That is, is provides a framework for writing Graphical applications under Microsoft Windows. EWin provides classes for most common Win32 tasks, such as creating and manipulating windows, managing multiple threads, and performing network operations via WinSock. It does not attempt to provide classes for everything that Windows can do... just a large number of very common things. (This is one way in which EWin differs from Microsoft's Foundation Classes.)
EWin requires a fairly modern Win32 compiler. It uses templates for storage classes (though it does not currently use the Standard Template Library's storage containers -- that may change soon). It uses the "mutable" and "explicit" keywords on occasion, and uses "const" everywhere. It does not currently use exception-handling at all. This may change, or not. Windows programming is not especially linear, so exception-handling is not nearly as big a win as it is for other types of programming.
EWin has been tested under Borland C++ 5.01, Microsoft Visual Studio 6, Metrowerks Codewarrior... 4? 6? I don't remember... and a few others. However, since I no longer have access to any compiler besides Microsoft Visual Studio, I would guess that the code body is no longer 100% compatible with these compilers. Any problems should be easy to fix.
I think the best way to get a feel for EWin programming is to jump into the tutorial and begin creating EWin programs. (The tutorial has more overview material.)