Torsten Manz has written an HP-15C simulation entirely in Tcl/Tk. It is is GPL'd, and available from:
[http://www.hpmuseum.org/simulate/15_1_201.zip]
The link above ist version specific. Generic link is http://www.hpmuseum.org/simulate/simulate.htm - Torsten
The version available from "The Museum of HP Calculators" is outdated. The latest version (1.2.09) is available on the simulator home page [L1 ]. This version also supports Windows Vista. Torsten