Welcome to the MSYS2 Wiki
Introduction - overview and important information
Installing and upgrading - required reading for all users
Re-installing from scratch - in case of unrecoverable problems
Building packages and contributing - how packages are built and how to make new ones
MSYS2 vs. Cygwin - differences and similarities
MSYS2 on Wine - how to install and use MSYS2 under Wine
Porting for MSYS2 or MinGW-w64 - useful resources and common issues
Package list - list of packages we provide
Launchers - various ways to launch MSYS2 shells
If you have any problems with the POSIX side of MSYS2 (e.g. ssh, home directories, user accounts, native symlinks, signal handling, ...), try to consult the Cygwin documentation first, as a lot of what's written there applies to MSYS2 as well.
There is also an excellent introduction from Matthieu Vachon describing MSYS2, the shells, pacman and other stuff in a less technical, more practical way.