Ninebrains
A desktop app that runs several Claude Code and Codex agents at once, each in its own git worktree, with an independent gate that proves the work before it counts as done.
What it is
Ninebrains is a free, open-source, local-first desktop app for macOS, Windows and Linux. It gives every coding agent a lane of its own — its own git worktree, branch, terminal, editor and browser — so four agents can run against one repository without stepping on each other's files. A central coordinator called the Brain holds the plan as a graph of jobs with dependencies and hands ready jobs to whichever lane is idle. It is a fork of Emdash by General Action, used under Apache-2.0, and it runs the user's own logged-in `claude` and `codex` CLIs rather than replacing them.
Why we built it
We run our own multi-agent builds this way: the rebuild of this site was fanned out across named agents, each in its own worktree, under this same discipline. One agent in one terminal is easy to follow; four sharing a checkout is not, and nobody was checking their claims before we read them. Ninebrains is that internal tool, opened up.
What it proves
That we build for multi-agent work rather than just writing about it, and that we hold our own agents to a gate instead of taking their word for it. Verification gates — tests, a three-width screenshot check, a read-only reviewer, citation checks — run before a job counts as done, and a failed gate sends the lane back with feedback for up to three attempts before it blocks.