Free42 – HP-42S calculator simulator

Free42 is a simulator of the Hewlett-Packard HP-42S scientific programmable calculator and the HP-82240 printer. It reproduces the behaviour of the original calculator while adding features that make it more convenient to use on modern computers.

Unlike emulators that require an original calculator ROM image, Free42 is a complete implementation written without HP code. It remains compatible with programs written for the HP-42S, including its Reverse Polish Notation (RPN) programming model.

Free42 supports scientific and statistical calculations, complex numbers, matrices and programmable operations. Programs can be imported and exported, removing the original calculator’s limitations on transferring software between devices.

The application also supports simulated printer output, configurable calculator skins and saving the calculator’s state between sessions. It runs on Linux, macOS, Windows, Android and iOS. Development remains active, with version 3.3.12 released in May 2026.

This is free and open source software.

Key Features

• Reimplement the HP-42S scientific programmable calculator without requiring a proprietary ROM image.
• Supports HP-42S-compatible programs and Reverse Polish Notation.
• Perform scientific, statistical, complex-number and matrix calculations.
• Import and export calculator programs for transfer between devices.
• Emulates the HP-82240 printer, with options for saving printer output.
• Supports configurable calculator skins and display settings.
• Preserve calculator state between sessions.
• Runs on Linux, macOS, Windows, Android and iOS.

Website: codeberg.org/thomasokken/free42
Support:
Developer: Thomas Okken
License: GNU General Public License v2.0

Free42 is written in C++ and C. Learn C++ with our recommended free books and free tutorials. Learn C with our recommended free books and free tutorials.

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