Free42 is a re-implementation of the HP-42S calculator and the HP-82240 printer.
It is a complete rewrite, not using any HP code, and it does not require an HP-42S ROM image.
Free42 is an Open Source project. The executables and source code are released under the terms of the GNU General Public License, version 2.
All third-party code used in Free42 is either in the public domain, or licensed under terms compatible with GPLv2, or used with the authors' permission.
From version Free42 2.0.23:
SOLVE now tries harder when secant extrapolation gets stuck due to the secant being excessively steep.

0^0 now returns Invalid Data, not 1, for all combinations of real and complex arguments. The rationale for returning 1 was mathematically questionable, and Invalid Data is what the real HP-42S returns.
All versions
February 9, 2019
January 26, 2019
January 13, 2019
January 13, 2019
January 12, 2019
June 24, 2018