MSYS2 is an updated, modern version of MSYS, both of which are Cygwin (POSIX compatibility layer) forks with the aim of better interoperability with native Windows software.
The name is a contraction of Minimal SYStem 2, and aims to provide support to facilitate using the bash shell, Autotools, revision control systems and the like for building native Windows applications using MinGW-w64 toolchains.
We wanted a package management system to provide easy installation of packages, and ported Arch Linux's Pacman. This brings many powerful features such as dependency resolution and simple complete system upgrades, as well as providing the build system (makepkg) which is used to make these packages. The set of software-building recipes (PKGBUILDs) for MSYS2 itself are at:
.. and those for MinGW-w64 (i.e. native Windows software) are at:
Both 32 and 64bit are supported.