OpenAI Codex CLI
OpenAI Codex CLI is an open-source terminal agent that applies natural language instructions to your local codebase. Running in your terminal, it reads files, writes code, runs tests, and iterates until the task is complete — powered by OpenAI's o4-mini model.
Gemini CLI
Google's open-source terminal coding agent powered by Gemini 2.5 Pro. Features a 1M token context window, native MCP server support, and is free to use within Gemini API limits. A direct Claude Code and Aider competitor from Google.