Greenify is an Android application that helps users to identify and put misbehaving apps into hibernation. It helps to improve the overall performance of Android devices by hibernating apps that are not in use. It efficiently manages apps which are running in the background and draining resources. It also helps in preventing the device from lagging and helps to reduce battery drain. It supports all major versions of Android and is available for free. It also has an optional donation version that adds additional features.
SD Maid helps with storage space, while greenify is all about battery optimization