Thanks to some help from HrastProgrammer, the HP-11C is now mostly functional in the Nonpareil simulator. Preliminary results indicate that the HP-12C, HP-15C, and HP-16C seem to work as well. The display annunciators don't work yet, and there are some anomalies to investigate before it's ready for a release.
Recently I've mostly been working on improvements to the simulation infrastructure. I've now got working code to save the state of any simulated calculator to a disk file as a gzip-compressed XML file, so Nonpareil will finally have continuous memory. :-) There's still some remaining work on restoring state from a save file, and making it automatically save on exit and restore on startup.
Dealing with compressed XML using libxml2 is very easy. It's a great library.