Aider is an open-source AI coding assistant that runs in your terminal and edits files in your local git repository. Unlike IDE plugins, it works through your command line - you describe what you want, and Aider makes the changes directly to your codebase, shows you the diff, and commits the result. It supports all major models (GPT-4, Claude, Gemini) and is configurable down to which models handle which parts of your workflow. The open-source nature means you can inspect exactly what it's doing and run it with any model API you have access to. For developers who live in the terminal and want AI-assisted editing without a proprietary IDE plugin, Aider is the most customizable and transparent option available.