Spec Kit
Open-source scaffold from GitHub that operationalizes spec-driven development with AI coding agents. Creates structured .specify/ folders that serve as the source of truth for Claude Code, GitHub Copilot, and Gemini CLI — steering AI generation from upfront specs rather than improvised prompts.
BMAD-METHOD
OSS spec-driven development methodology and toolkit. 46.7k stars by May 2026. Defines a structured Build–Measure–Architect–Document loop with templates that AI agents (Cursor, Claude Code, Aider) can follow deterministically.