FreeTube
FreeTube is a free and open source, multi-platform, privacy-focused YouTube desktop client
MoonPlayer
MoonPlayer is a free and open source video player for playing and downloading online videos from YouTube, Youku, and iQiyi, as well as local videos
SMTube
SMTube is a free and open source program for searching and watching YouTube videos
Musictube
Musictube is a free and open source program to listen to music/songs from YouTube
Kaku
Kaku – free and open source music player supports different online platform like YouTube, SoundCloud, Vimeo and more
Vocal
Vocal – free and open source powerful, beautiful, and simple audio or video podcast client
Minitube
Minitube – a simple software for viewing videos from YouTube: just enter the search keyword and Minitube will output an endless video stream
Gnome Twitch
Gnome Twitch – free and open source software allows searching for and watching Twitch streams from the desktop for Linux
Stremio
Stremio – organize and watch videos, movies, TV series and TV channels from different services: Youtube, iTunes, Amazon, Netflix, Twitch and others