GitHub Copilot is the most widely used — it integrates into VS Code and most IDEs. Cursor is growing fast as an AI-first editor. Both dramatically speed up development.
GitHub Copilot is free for students and open-source maintainers. For individuals it costs $10/month. There is also a limited free tier available.
AI can write substantial portions of applications but still requires human oversight for architecture, security and edge cases. It's best used as a pair programmer rather than a replacement.