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OptiPNG vs Curtail: catalog facts
OptiPNG	Curtail
Free Free and open source under the zlib licence.	Free Free and open source under the GPL-3.0-or-later.
Windows, Command line	Linux
Lossless recompression of PNG files Converts BMP, GIF, PNM and TIFF to optimized PNG	Handles PNG, JPEG, WebP and SVG Uses proven tools like oxipng and pngquant
Command line only, no graphical interface Lossless only, so savings are smaller than lossy tools	Linux only Compression only, no other editing
Downloadable app	Downloadable app
Open source	Open source
License: Zlib	License: GPL-3.0-or-later
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 1, 2026

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