SpeedCrunch
I wanted to like this, but when I tried it on Windows, setting the font size and/or color theme made the input bar/expression editor disappear.  Absolutely nothing would bring it back, not changing the settings back or even uninstalling and reinstalling.  I assume it works better in a linux.(I'd report a bug, but  a calculator program making itself unusable in less than a minute with steps I can't precisely recreate kinda kills my enthusiasm for that process.)