A tool any handyman shouldn't be without
Gadget Box is an incredibly useful junk drawer of tools, ranging from levels, rulers, protractors, compasses, and more. It might not look especially pretty, but damn is it useful. There’s a unit converter in there, which, though also built into the native calculator app, is handy for those doing construction and using the other tools anyway.
There’s tool which uses a bit of trigonometry to determine the height of something based on how far you are from your subject and how much you tilt the device when picking targets at its base and top. There’s even a custom flashlight app in there that lets you set flash frequency of the camera LED, or change color on the screen. Handymen, you’ll want this app in your toolbox.