In short: it's a free C and C++ compiler for Microsoft Windows.

GCC (GNU Compiler Collection) is a free and open source compiler for C and C++ (and other languages like Objective-C, Fortran, D).

MinGW-w64 is a free and open source C library for targetting Windows 32-bit and 64-bit platforms.

The combination of these results in a free C/C++ compiler for Windows.

Even though GCC and MinGW-w64 can be used on other platforms (e.g. Linux) to generate Windows executables, the WinLibs project only focusses on building versions that run natively on Windows.

Also some additional tools are added, including:

• GDB - the GNU Project debugger
• GNU Binutils - a collection of binary tools
• GNU Make - a tool which controls the generation of executables and other non-source files
• Yasm - The Yasm Modular Assembler Project
• NASM - The Netwide Assembler
• JWasm - A free MASM-compatible assembler
• LLVM/Clang/LLD/LLDB - The LLVM Compiler Infrastructure

This is a standalone build, which means this download offers a complete compiler environment for Windows.