GPT Engineer creates entire applications from prompts. Describe an app and GPT Engineer generates the full codebase with proper structure, dependencies, and deployment configuration. Features include iterative refinement through conversation, clarifying questions, file generation, dependency management, and improvement suggestions. Unlike simple code generators, GPT Engineer understands application architecture and creates production-ready structure. Open source with both CLI and web versions. Can generate web apps, APIs, scripts, and more. Popular for rapid prototyping, MVPs, and learning how applications are structured. The AI maintains conversation context for iterative improvements.