Greenify - Suspends apps to keep them from draining your battery. Its different than an app killer, which completely shuts down the app.

Flush - Find out were public toilets are and how they rate.

Manual Camera - Better than the stock camera imo.

SD Maid - (Root) Clean up your phone and free up extra space.

Smart Wifi Toggle - (Root) Turn on and off your Wifi based on cell towers.