Agent Skills, maintained by Addy Osmani, is a set of packaged engineering skills (MIT licensed, 24 skills) covering the full DEFINE→PLAN→BUILD→VERIFY→REVIEW→SHIP lifecycle: idea refinement, specs, implementation, testing, QA gates, and shipping. Works with Claude Code, Codex, Cursor, Copilot, Windsurf and 70+ coding agents, installable with one command.