Greenify - Greenify is a mobile app that gives you greater control over your Android device's power usage, allowing you to get a lot more mileage out of your battery life without having to constantly plug it back into a charger.

island - a free and opensource alternative to parellel space

DU Battery Saver - DU Battery Saver, get up to 50% more battery life for your Android phone. Battery Saver learns how you use your phone, then creates smart profiles that match your settings to your needs while getting more life from your battery.

App Cloner - Clone your Android apps so you can use multiple logins.

Accubattery - Monitor's battery capacity through the use of science

Parallel Space - Parallel Space – Multiple accounts and Two-Face is free to use mobile app that helps you clone or run multiple accounts of the same app simultaneously, and use themes to style your unique space.