This is some nice calculator which is grate from all aspects. But probably coolest thing here that retro looking Nixie display and old style keyboard keys are fused with modern electronics such as Raspberry Pi.
Raspberry Pi is definitely an overkill for such calculator, but since these things are getting cheaper and cheaper, so why not? To use a bit more of Raspberry Pi power Scott made it internet connected calculator where you can send calculations to WolframAlpha. All parts of calculator is custom made where each nixie tube is controlled by K155D driver chip. Each chip is controlled through I2C IO expander that is connected to Raspberry Pi. Custom power supply board takes care of powering computer with 5V and tubes with high voltage. I’d say this is quite and effort to build a calculator.