A less useful calculator: The traditional bead and frame device, faithfully displayed on the PalmPilot.
I'm releasing this as freeware (with source, too).
It's avaliable in several formats:
The abacus program as a
gzip'd tar file
The abacus program as a
zip file
The abacus
prc file
The abacus sources as a
gzip'd tar file
The abacus sources as a
zip file
Up to my PalmPilot page