Monolithos is a local-first AI operating system designed to serve as a personal agent substrate that users fully own and control. It combines a structured memory layer, multi-model AI chat (supporting Gemini, Claude, and Grok), and native document, presentation, and data engines into a single cognitive platform. The system is Obsidian-compatible, keeping all data on the user's own device with no mandatory cloud dependency. Monolithos supports external AI agents connecting via MCP federation, and includes features such as a background memory crystallization engine and a multi-language podcast/audio engine.