Square Open Source contributes internally-developed libraries for Android, iOS, Java, Go, and JavaScript back to the community.

curl is a command line tool and library for data transfer used by virtually every Internet user

Hoppscotch is an open source API development tool for creating requests faster and saving precious time on development for software engineers.

Ktor is an open-source, lightweight framework for building asynchronous servers and clients in Kotlin for microservices and RESTful APIs.

REST Assured is an open-source Java library designed to simplify testing and validating REST services, making API testing in Java as easy as in dynamic languages.