CygWin

CygWin uses a completely different approach to offer a level of Linux compatibility on Windows. It is basically a library that emulates offers a large subset of the POSIX APIs, and much Linux software can be rebuild against this library. The resulting binaries are regular Windows binaries and not Linux binaries, which also implies that the Windows shared library approach is used rather than the Linux one.

CygWin also comes with a large range of recompiled GNU and other Open Source tools.

Since the binaries are regular Windows binaries, they can be started directly from any Windows shell (cmd.exe or PowerShell) and can be mixed with regular Windows executables easily.

As CygWin programs are really Windows programs, they also see the same file systems as any other Windows program, though the CygWin translation layer will convert the paths into a more UNIX-like one, e.g., using the forward slash instead of the backslash and a different way of showing drive letters.

The downside is that even source-level compatibility with Linux is certainly not as good as in WSL 1 or 2, and that certain Linux functionality which is not well supported by the Windows kernel may come with a performance hit. Also, it cannot run native Linux x86 binaries, neither 32-bit nor 64-bit ones.

CygWin is also used internally by some of the software packages that we will mention in the Software chapter.

There are other commercial products that use a similar approach, e.g., the PTC MKS Toolkit.