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x11-calc vs Free42: catalog facts
x11-calc	Free42
Free Free and open source under the GPL-3.0-or-later licence.	Free Free and open source under the GPL-2.0 licence.
Linux	Windows, macOS, Linux, Android, iOS
Faithful simulation of many HP calculator models Runs original firmware for accurate behaviour	Runs existing HP-42S programs No HP ROM image required
Niche audience familiar with HP calculators Linux-focused distribution	RPN keystroke interface has a learning curve for newcomers Modern extras such as plotting are in the separate Plus42 project
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0-or-later	License: GPL-2.0
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 1, 2026	Official website Full listing and sources Checked October 2, 2026

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