MediaHuman YouTube to MP3 Converter - Extracts MP3 audio from YouTube, Vimeo, Dailymotion, Mixcloud, Bandcamp, SoundCloud and many others. Available for macOS, Windows and Ubuntu/Linux. FREE!
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.
Video DownloadHelper - Browser extension to download videos from the Web
4k Video Downloader - 4K Video Downloader is a software program that helps people download video files from sites such as Facebook, YouTube and Dailymotion.
ClipGrab - A friendly downloader for YouTube and other sites
yt2mp3.org - Free online YouTube to MP3 Converter