cmux: Open-source macOS terminal for AI coding agents, with vertical tabs and notifications

cmux is an open-source macOS terminal built on Ghostty, written in Swift and AppKit rather than Electron. It reuses libghostty for GPU-accelerated rendering and reads themes, fonts and colors from the existing ~/.config/ghostty/config. Its core additions are a sidebar and notification system: per-workspace vertical tabs show git branch, linked PR status and number, working directory, listening ports and the latest notification text; when an agent waits for input the pane gets a blue outline, the tab lights up, and ⌘⇧U jumps to the most recent unread item. Notifications are captured via the terminal sequences OSC 9/99/777, and a cmux notify command can be wired into agent hooks for Claude Code, OpenCode and others. It also includes a scriptable browser pane ported from agent-browser, letting agents snapshot the accessibility tree, grab element references, click, fill forms and run JS against a local dev server. A CLI and socket API support creating workspaces, splitting panes, sending keystrokes and opening URLs; cmux claude-teams runs Claude Code's teammate mode in one command without tmux, with teammates appearing as native splits with sidebar metadata and notifications. For developers running multiple Claude Code or Codex sessions, these features turn 'which agent needs me' from tab-flipping into clear visual signals and a notification pane; SSH workspaces route the browser pane over the remote network with localhost directly usable, and dragged images upload via scp. Session restore saves window layout, working directory, terminal scrollback and browser history, but does not checkpoint arbitrary running process state, so users needing live connections across exits, crashes and updates can opt for a local tmux or zellij owner. The project is GPL-licensed and free and open source.