OGS - Play go/weiqi/baduk online
KaTrain - Improve your go by training with KataGo.
qGo - Go is an ancient boardgame, very common in Japan, China and Korea.
GNU Go - GNU Go is a free program that plays the game of Go.
SmartGo - Software for the game of Go, with apps for iPhone, iPad, Mac, and Windows.
Sabaki - Sabaki is cross-platform graphical UI for Go/Baduk/Weiqi game board and SGF (Smart Go Format) editor. Free, open source, based on Electron.