NewPipe is a lightweight YouTube front-end for Android.
It doesn't need the YouTube-API or any Google Play Services, as NewPipe only parses the YouTube website in order to gain the information it needs.
Therefore this app can be used on devices without Google Services installed. Also, you don't need a YouTube account to use NewPipe, and it's FLOSS.
Display general information about a video
Watch YouTube videos
Listen to YouTube videos (experimental)
Select the streaming player to watch the video with
Download audio only
Open a video in Kodi
Show Next/Related videos
Search YouTube in a specific language
Watch age restricted material
Display general information about channels