Simulators for the hp15c and hp16c calculators, can be used in the browser or as Android app(lication).

Program to determine the calibration value needed to correct for the frequency error of dm42s' RTC.

The HP 48 object listed below in ->ASC form is a high-performance polynomial root finder. Those of you who remember the HP 71B Math Pac will recognize this as the same as the PROOT command from that Pac; it is in fact the same assembly-language code, given an RPL front end to operate in the HP 48.
Found on https://www.hpmuseum.org/forum/thread-10967-post-160700.html#pid160700
See also http://www.jeffcalc.hp41.eu/emu71/mathrom.html#src for the uncommented source code of PROOT and other functions of the HP71B math pack.

HP-15C Simulator for Windows, Linux and macOS. Supports data exchange with SwissMicros https://www.swissmicros.com DM15 models.

Perl program to convert {dm,free,HP}-42 programs from textual representation to raw files which can be loaded into {dm,free}42.

Free42 is a re-implementation of the HP-42S Scientific Programmable Calculator and HP-82240 Printer.
It is a complete rewrite, not using any HP code. 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.

A Hewlett Packard Infrared Signal Decoder
Martin Hepperle
June 2015
Several Hewlett Packard pocket calculators are able to send printer output via Infra-Red (IR) signals to a small portable printer. They use an HP-specific transmission protocol which is also called “Red Eye”. This protocol is different from the better known IrDA protocol. This document gives a brief overview of the format and describes hard- and software to build a decoder system for this protocol.
This system allows receiving the “Red Eye” signals with a computer via a serial or an USB interface.

Links and recommendations for books about astronomical algorithms.

The world's smallest programmable RPN calculators ever. The complete family DM-11, DM-12, DM-15 and DM-16.

Web-based simulator of the hp15c calculator. Enhanced version with stack display. Note that contrary to emulators such as nonpareil, this simulator does not produce the same results as the real hp15c.