CSIM is a simulator for the HP-35, HP-45 and HP-55 "Classic" series of calculators from Hewlett-Packard. It is based on Eric Smith's CASMSIM.
CSIM runs on all Palm OS® devices. The current version is 0.5, based on CASMSIM version 0.14. It is available as a PRC file or as source code in a tar.gz file under the terms of the GPL.