Any of you have an app you use all the time that most don't know about or use?

I just found an app called hopper that helps you know when to book flights and lets you know when the best time to book is. We are going on a cruise this summer so I used it to book our flights to Orlando.

Other apps I use daily: Google Calendar, yahoo sports app (best sports app), Google photos (free photo storage) and IFTTT. I have this one setting with IFTTT that allows me to press a button on my phone and my phone will ring about 15 seconds after. I use it every day when my boss wants to come in and talk about who knows what.