CASMSIM is a microassembler and simulator package for the Classic series of HP handheld calculators. It is written in C and uses the GTK+ toolkit.
An emulator of the HP 67 calculator in two versions: one in the form of a CDA for the Apple ][GS, the other as an ncurses-based program running under UNIX, designed and tested on Linux.
nsim is a microcode-level simulator for the HP-41CV programmable scientific calculator. It is written in C and uses the X window system for display. To date, the focus of development has been simulation accuracy rather than appearance.
A free TI85 calculator emulator for Unix/Linux. It's based on the MSX Z80 emulation library and the FLTK toolkit.
An emulator for the TI92, a powerful calculator from Texas Instruments.
The x48 is an emulator of the Saturn Processor and the I/O of an HP48 calculator. There is a debugger for the Saturn Processor.