This app was mentioned in 6 comments, with an average of 23.33 upvotes
Apple has a lot of agendas.
For example, they don't allow any GPLv3 open source software, because Apple's "absolutely no sideloading" policy is incompatible with GPLv3. They don't allow emulators, who knows why. They tried to ban Steam in-home streaming app. Their developer licenses cost enough to discourage anyone from releasing completely free and ad-free apps, and as a result, high quality free apps are a rarity in iOS store. Try finding something like this free calculator app in iOS store, and you'll see it.
None of that would be an issue if users were free to load their own apps, but they aren't.
I personally like this one, because once you close it it gives you a Facebook messenger-like floating icon that gives you a clear calculator. SUPER handy, as you don't have to keep switching apps/copying/pasting. Just turn on floating calculator from the settings>actions. It's also got some advanced fancy graphing shit. I believe it's what used to come with Cyanogen Mod and used to be developed by Clockwork? I could be wrong.
An alternative for Samsung users is the calculator for the Edge panel, but I personally prefer the floating calculator.
https://play.google.com/store/apps/details?id=com.xlythe.calculator.holo is also the best calculator in the market.
Again, doesn't spy or send data. It just does one thing, and does it really well. Also has a history of your last sums which is why I use it and disable stock. Based on old android stock app
In Google maps, turn location history on. You now have GPS records of where you have been. Handy for an alibi, or time sheet tracking.
SwiftKey keyboard, slide finger from letter to letter to type.
Moonreader Pro - books on your phone.
Reddit is fun - best app for android I've come across.
Also toggle settings in your notifications bar, all phones have a default flashlight widget and other handy shortcuts. If I was rooted I'd be reconfiguring the home button to toggle light on/off on long press but have used button remapper to press camera button twice for flashlight.
Tasker if you like to get complex. Automate your phone. Automate your home with your phone. Automate the interface with your smart devices from your phone.
Can also offer advice on home networking (everyone has shitty WiFi).
For example, I use this calculator. It's powerful and configurable - way better than any of the standard apps the devices are usually shipped with, and it's completely free. No ads, no microtransactions.
I'm pretty sure there is no free app that offers the same functionality on iOS, as even flashlight apps there come packed with ads and "remove ads" microtransactions.