peterb. A couple of recommendations
Textra - Recently became a paid for app if you want it ad free (61p) but it's a fantastic text message app and allows you to send group messages (which last time I checked Hangouts couldn't do, even though it's such a basic feature)
QuickPic - Image browse that uses the entire screen to show thumb nails (as opposed to around 3/4 the screen in the default "Photos" app. Also allows you to temporarily rotate the photo with 2 finger rotate motion on the screen when browsing photos (without altering the original file) - very useful when the photo didn't save in the correct orientation.