Soulver

A cool take on a calculator app for iPhone/iPad/Mac, which recently had a big version 4 upgrade. Instead of a single register to work with, you get a vertical multi-line notepad where you not only can do individual calculations on each line (as a mix of words, numbers, and units, if you want) but can also then perform operations that include or refer to results from other lines, plus it can do things like perform currency and unit conversions, calculate how many days there are between two dates (or between, say, now and Christmas), and tell you how far apart two cities are. It’s more powerful than a regular calculator while also being more friendly and flexible than a spreadsheet, since it takes natural-language input (e.g., if you want to get X as a percentage of Y, you can enter “X as a percentage of Y” and it will give it to you). If you need to quickly add or multiply or do whatever to a bunch of numbers you’re looking at, you can also use dictation to just say what you want, which can be a lot faster and easier than typing it out.

It’s also a one-time purchase, not a subscription (with a 60-day free trial available to try it out, and options to buy it just for iPhone or for iPhone+iPad+Mac). There is a subscription option for advanced features that incur separate costs to access the necessary data/service (weather, stocks, and Wolfram|Alpha), but I imagine most people won’t specifically need those.