Aider is a command-line AI pair programmer that makes direct edits to your files. Works with any LLM (GPT-4, Claude, local models), uses git to track all AI changes, and allows you to review, commit, or revert easily. Chat with AI about your code and Aider makes actual edits rather than just suggesting. Features include multi-file editing, git integration, repository context, cost tracking, and works with any project. Being terminal-based, it integrates into existing development workflows without changing your editor. Popular with developers who prefer terminal workflows and want AI that makes real changes responsibly.