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Mayo vs fstl-e: catalog facts
Mayo	fstl-e
Free Free and open source.	Free Free and open source under the MIT licence.
Windows, macOS, Linux	Linux
Converts between STEP, IGES, STL and other CAD formats Clip planes, exploded views and measurement	Opens STL files quickly Configurable background
A viewer and converter, not a modelling tool	Viewer only, no editing Small fork maintained by one developer
Downloadable app	Downloadable app
Open source	Open source
License not stated	License: MIT
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked October 1, 2026

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