Postman is the API client that grew from a Chrome extension in 2012 into a full API development platform — collections, environments, automated testing via Newman, mocking servers, API documentation, and team collaboration. Most engineers use it primarily as a tool for exploring third-party APIs and testing internal endpoints during development.
The competitive landscape has changed: Bruno (open-source, file-based collections), HTTPie Desktop, Hoppscotch, and Insomnia compete for the same role with different philosophies on cloud sync, scripting, and team workflows. Postman's strength is breadth of features; the weakness is the increasingly account-required and cloud-first product direction.