Re: I slapped a wireless card into an HP laptop...
For a RPN calculator, search for SwissMicros. They make clones of the classic HP RPN calculators (HP 15C, HP 42C, HP 41S, etc) with firmware from the open source Free42 project. They even have tiny credit card-sized versions of the HP15C.
I nearly bought one, but hesitated because I already have my dad's 1980s HP 15C (still running on the original batteries!) and the Touch 11i Free app on my Android phone.