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