Minitube - Minitube is a YouTube desktop application.
YouView - Browse, watch, convert, and download YouTube videos on your Mac faster, because YouView uses the core technologies of Mac OS X to play instead of Flash allowing video to run smoother on systems with lower specs.
Tubbler - YouTube Movie Player for Mac OS X.
MuzicGenie - Hassle free, Endless and Unlimited music from Youtube videos.
Muziic - Muziic Player puts millions of songs right on your desktop - free and legally.
NewPipe - NewPipe is a lightweight YouTube front-end for Android.