CONV. - Convert YouTube video to MP3, GIF or MP4
4k Video Downloader - 4K Video Downloader is a software program that helps people download video files from sites such as Facebook, YouTube and Dailymotion.
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
Video DownloadHelper - Browser extension to download videos from the Web
Yout - YouTube to Mp3 Converter
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.