NewPipe

Features
Watch videos at resolutions up to 4K
Listen to audio in the background, only loading the audio stream to save data
Popup mode (floating player, aka Picture-in-Picture)
Watch live streams
Show/hide subtitles/closed captions
Search videos and audios (on YouTube, you can specify the content language as well)
Enqueue videos (and optionally save them as local playlists)
Show/hide general information about videos (such as description and tags)
Show/hide next/related videos
Show/hide comments
Search videos, audios, channels, playlists and albums
Browse videos and audios within a channel
Subscribe to channels (yes, without logging into any account!)
Get notifications about new videos from channels you're subscribed to
Create and edit channel groups (for easier browsing and management)
Browse video feeds generated from your channel groups
View and search your watch history
Search and watch playlists (these are remote playlists, which means they're fetched from the service you're browsing)
Create and edit local playlists (these are created and saved within the app, and have nothing to do with any service)
Download videos/audios/subtitles (closed captions)
Open in Kodi
Watch/Block age-restricted material