Nacre is a self-hosted knowledge index for AI agents, where permission is part of retrieval rather than a filter bolted on after it. An agent acts for a person and reaches only what that person may read: the access check runs inside the index traversal, so results are never trimmed afterwards. Connect over MCP or REST, run it with Docker in two minutes, keep every document on your own machine. Apache 2.0 - and a live demo where one query gives three people three different answers.