ACP is a self-hosted daemon (Go, `coordd`) giving multiple agent harnesses on different machines a shared, content-addressed filesystem plus a comms layer: directed mailbox, totally-ordered event log, CRDT co-editing, TTL leases with fencing tokens, and full version history with restore-as-forward-commit. Multi-tenant via "spaces," HA via 3-node Raft with mTLS and encryption at rest, TLS on 8443 out of the box. There's an MCP bridge for Claude Code/Codex, a TS/JS SDK with zero runtime deps, and capability negotiation through `/v1/healthz`. The engineering details are unusually considered: bulk-delete guards (HTTP 428 until you confirm exact counts, ordinary writer tokens denied bulk ops entirely), scoped read tokens designed so out-of-scope paths are indistinguishable from missing ones (no existence oracle), and presence data that self-expires and never touches durable storage. The RFC-style extension process is a nice touch. The caveat a practitioner must weigh: this is a *client* repo. Install scripts, binaries, docs — the implementation source is private, so you're trusting prebuilt releases from a 3-star repo whose contributors include a Claude and what appears to be a VC. `curl | bash` into that is a faith-based deployment. Presumably the agents will coordinate on the RFC for whether agents should be allowed to coordinate.