I've tried a couple of simpler calculators before: Numi and Soulver. This one is a lot more powerful, naming just a few things that make it great:
- It's symbolic: instead of just calculating the result, it treats expressions as first-class entities — so you can solve equations, find function derivatives, etc
- It's functional: it not only has functions, it also treats them as first-class entities — so you can pass a function as an argument to another function (though this one probably doesn't make much sense for anyone who is not a software engineer or a mathematician, but whatever)
- It works with matrices, plots, has a ton of built in measurement units, etc
- Oh, and it supports mobile platforms and synchronizes your sheets via iCloud
That being said, there are some problems and enhancement options, that I hope the developer(s) would eventually give some more attention:
- The "undo" after inserting "=>" doesn't erase the computed answer, so you have to remember not to use it in these cases and just remove the text manually instead.
- There are missing currencies, like georgian lari.
- There's no configuration at all. I wouldn't expect some advanced customization, but simple things like changing the color scheme or fonts would be nice. But most important of all, vertical tabs!
- Would be nice if the scroll went down over the last line, so you don't have to look at the bottom of the screen if you are editing the last line.
- (iPad) Inserting numbers is broken if you are using an external keyboard.
Best of luck to the developer(s) and thanks for your work!