Calculator app + Tapbots = …
This calculator/ unit converter focuses on design and usability. It boasts a basic and scientific mode, but subtly rethinks conversions and the history tape. The former can exist as a row above the main display, and you can configure which units are included; click the conversion to see a popup with further calculations. The tape replaces a memory button with favourites, which enable you to later work with a result or the expression that composed it.
The app looks good, dialing down transparency compared to Apple’s horrible OS X Yosemite Calculator, although some button text is grainy on non-Retina displays. We also liked the expression view, showing what you’ve typed before hitting ‘equals’, but it’s a pity you can’t edit anything from the path in a manner similar to Soulver. Still, Calcbot is a pleasure to use and comes recommended. Craig Grannell
Sandwiched between Apple’s free Calculator and PCalc, but much better than the former.