Stoplight
Design-first platform for creating, governing, and documenting OpenAPI specifications. Bundles a visual editor, Spectral (JSON/YAML linter), Prism (mock server), and Elements (docs renderer) into one workflow. Teams use it to enforce API style guides across large API portfolios.
Redocly
Combines Redoc (25k+ GitHub stars) with a powerful CLI for linting, validating, and bundling OpenAPI specs. Supports OpenAPI 3.x, Swagger 2.0, AsyncAPI, and Arazzo. Enterprise offering adds developer portals and auto-generated code samples across teams.