Datasette : Datasette provides an instant, read-only JSON API for any SQLite database. It also provides tools for packaging the database up as a Docker container ...
pump.io : Social server with an ActivityStreams API. It's a stream server that does most of what people really want from a social network.
History.js : History.js gracefully supports the HTML5 History/State APIs (pushState, replaceState, onPopState) in all browsers. Including continued support for dat...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Freebase : A community-curated database of well-known people, places, and things
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.