Postal : Postal is a complete and fully featured mail server for use by websites & web servers. Think Sendgrid, Mailgun or Postmark but open source and ready f...
OpenCalais : Calais is a rapidly growing toolkit of capabilities that allow you to readily incorporate state-of-the-art semantic functionality within your blog, co...
Freebase : A community-curated database of well-known people, places, and things
JSON API : A specification for building APIs in JSON. Clients built around JSON API are able to take advantage of its features around efficiently caching respons...
httpbin.org : A simple HTTP Request & Response Service.
Bluepine is a DSL for defining API Schema/Endpoint with the capabilities to generate Open API (v3) spec, validate API request and serialize object for API response based on single schema definition.