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Postman vs ATAC: catalog facts
Postman	ATAC
Freemium A free tier covers individual use with limits on collaborators, collection runs and…	Free Free and open source under the MIT licence.
Windows, macOS, Linux, Web, Browser extension	Windows, macOS, Linux, Command line
The most widely used API client, so collections and tutorials for it are everywhere Collections with environments, pre-request and test scripts, and a built-in runner	Full API client inside the terminal Optional Vim key bindings
Built around a cloud workspace, and an account is effectively required Offline and local-only use has become harder over successive versions	Still working toward its 1.0 release No graphical interface for people who prefer a mouse
Downloadable app, Web application, Browser extension	Downloadable app
Closed source	Open source
License not stated	License: MIT
Account needed	No account needed
Needs internet	Not stated if it works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.