An RPN calculator is a must for almost everything I do, from real engineering, to startup finances and expenses, to making/3D printing, to home/landscape improvement. I keep a real HP emulator* pinned to the taskbar at all times, ready to be launched and used with just a touch (and yes the touchscreen works great with the emulators, if you upsize them a bit. Plus, an actual HP-41cv on my physical desktop, for the heavy lifting not easily handled by the emulators. (Anything that can't be done on the HPs is going to need some code written, anyway...)

*Three, actually - an HP-15C Scientific pinned to the taskbar, and the default install links to the HP-12C Financial, and HP-16C Hex/Binary emulators in the apps menu. All are official exact HP emulations for Windows published by HP France some time ago. Alas, the link I had is dead, so I'm not sure where you can get them anymore...