This app was mentioned in 2 comments, with an average of 1.50 upvotes
I've been using DM Minion for a couple games. It works pretty well to keep combat moving but you have to go through a couple extra steps if you want to roll your own dice instead of let its RNG do the math for you.
https://play.google.com/store/apps/details?id=air.com.goatheadsoftware.lite.dm5e
To keep track of initiative order, I recommend DM Minion (I think they also has an iPhone app). It lets you load up monsters and players, and sort them according to their initiative, as well as helping you keep track of their condition.
They also has a paid app, that lets you create encounters above challenge 2. Also, this app, together with their website, lets you display the turn order on cellphones, laptops and tablets, letting your players keep track of the combat too (it hides a lot of info from them).