There’s something very retro about an RPN calculator with a 7 segment LED display - it’s programmable too, and offers complex numbers, matrix functions as well as numerical integration. Quite the project: Arduino-powered, unsurprisingly. A semi-flexible printed cover over tactile switches is a nice approximation to a calculator keyboard.
This 7 segment version (IVEE7) is a follow-on (and a cost-reduction) of an OLED version (IVEE) which also offers graphing facilitites:
Via hpmuseum forums