OGS - Play go/weiqi/baduk online
qGo - Go is an ancient boardgame, very common in Japan, China and Korea.
KaTrain - Improve your go by training with KataGo.
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.
Crazy Stone 2013 - Competitive Go software currently ranked at 6 dan.