Pixiv API for Python

Interactive Brokers TWS API

Lichess API documentation and examples

An OpenAPI description for GitHub's REST API

a wrapper SDK of FIX API, provides clients with a fully functioning programmable API into the FXCM trading platform, including streaming live price, get historical price and live trades.

binance-java-api is a lightweight Java library for the Binance API, supporting synchronous and asynchronous requests, as well as event streaming using WebSockets.

Official Documentation for the Binance APIs and Streams

Twitter4J is an open-source Java library for the Twitter API.

A collective list of free APIs