Ninebrains
A desktop app that runs several Claude Code and Codex agents at once, each in its own git worktree, with a 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.