Zerostack is a lightweight coding agent that connects to multiple LLM providers (OpenRouter, OpenAI, Anthropic, Gemini, Ollama) to autonomously edit code, run terminal commands, and search the web. It provides a crossterm-based terminal interface with markdown rendering, a configurable permission system with five modes, session save/resume with auto-compaction, and MCP server support for extended tooling. The project includes subagent design for parallel task execution and an integrated Exa search for web-based tools.