Some of mine are:
FitBit-the app syncs to my FitBit and tells me several details about my health beyond just how many steps I've taken. It also monitors my heart rate, my sleep, and I can use it to track water or food (I don't, but I could lol)
Runkeeper: I use this app to track my walks. It tells me how fast and long I walk and the path I take.
Kindle app: I read a lot of my books on Kindle now. I still love a paper book, but since Kindle books are often cheaper and take up less space, I get many of my books that way (especially fiction books)
Hoopla app: this is an app I have through the Enid Public Library. It allows me to check out up to four items per month at no charge and with no waiting list (the library often has waiting lists for their e-books). I use it a lot for audio books and some times for e-books. You can also check out movies and music.
Bible app: I use this when I'm doing my bible studies because it makes looking up verses so much simpler. It also has some great devotionals (for free-I like free)
Podcast app: I love listening to podcasts when I"m exercising so I use this app all the time.
Best Fiends: this one is kind of silly, but it is the only game app I have on my phone. It's a great way to spend a few minutes winding down but also a great way to get sucked into something mindless, so I have to be careful lol.