If you look closely it appears to be a fullscreen iTerm2 running a fancy tmux powerline. Edit: From https://github.com/koekeishiya/kwm/issues/8#issuecomment-16

If you look closely it appears to be a fullscreen iTerm2 running a fancy tmux powerline. Edit: From https://github.com/koekeishiya/kwm/issues/8#issuecomment-166593294 https://github.com/koekeishiya/kwm/issues/8#issuecomment-166... "The Apple menubar is hidden using the option that was added with El Capitan. I'm using the program nerdTool to create the illusion of a bar that you see in the screenshot."