Ion is a coding harness that runs entirely in a Chromium tab with no install and no terminal.

One agent.html file you open in a Chromium-based browser and point at any OpenAI-compatible server. The constraint is the pitch: it works only inside a folder you grant via the File System Access API, has no MCP and no terminal, so it cannot reach outside that folder, with checkpoints to revert file changes (GitHub). The author frames it as deliberately weaker than Pi, for quick edits including from a phone browser. Capability-limited by construction beats sandboxed after the fact, and eight stars on day one means nobody has stress-tested it.