Google Maps. My job requires that I go to new places almost every day, and we cover a large territory (about 22M people), so Maps is a key part of my day - though Google Calendar is a close second.
I also have about a dozen less-known apps that I use very frequently in my day job as an Audio/Video Systems Integrator. While for some things it wouldn't be my first choice, in a pinch, I could do just about everything from my phone.
There are 4 apps, Kik messenger (keep texting my Boyfriend ❤️💋) my bank app, my safari browser & Facebook messenger to text my best friend. I'm not one of those people that keep downloading apps & I don't buy iPhones when they make new ones.
My company has an app that lets me track inventory from a company smartphone. It's incredibly useful and I couldn't do my job without it. Aside from that I don't use any apps nor do I own a smartphone that leaves the workplace.
I despise cellphones and the accessibility they give others to your every waking moment. My time is my time. Want to track me down? Call me at home and leave a message on my answering machine.