zeet

Realcalc has an excellent RPN mode (enabled through Calculator Type in Settings). I’ve used it for the last six years or so (technically, in the premium version of the app).

Edit: Not open source - sorry, didn’t see the community!

I work in a university. Our web based services bork surprisingly frequently after Chrome updates and the IT Helpline’s go-to response is ‘have you tried turning it off and on again Firefox?’.