tl;dr: Juggler is an open-source GUI coding agent from JUCE creator Julian Storer that replaces the typical linear chat transcript with a tree-based, Miller-column interface for inspecting, branching, and editing LLM sessions. Built in Go with Wails (not Electron) and a JavaScript extension system where tools, strategies, and slash commands are all pluggable, it runs as a local server that multiple desktop and browser clients can attach to simultaneously. It supports Claude, OpenAI, Gemini, Ollama, and other providers, and is AGPLv3-licensed.