Free YouTube Download is the most popular YouTube downloader application now, released in 2006 and updated on a regular basis. It lets you download and convert YouTube videos, so you can watch them whenever you want.

Instructions (step by step)
Download and run the app
Copy YouTube URL and click 'Paste' button
Click the 'Download' button and enjoy!
Download videos in bulk!
Save entire YouTube playlists, user channels, videos from personal playlists (History, Liked, Favorites, Watch later), videos from different categories.
Download videos super fast!
Free YouTube Download is known for its lightning fast multistream downloading.
It allows you to download several videos in original quality in just a few seconds.

Features
get YouTube stream in any format, choose between MP4, MKV up to 8K UHD, WEBM, and MP3
perform conversion to MP4, AVI, and MP3
apply output name format patterns
open lists of links from any text files
transfer videos to iTunes automatically and convert them to iPhone / iPad / iPod
download subtitles