Great Downloader easy to use can convert into multiple file formats. Fast and impressive
Video DownloadHelper - Browser extension to download videos from the Web
yt2mp3.org - Free online YouTube to MP3 Converter
youtube-dl-gui - A cross platform front-end GUI of the popular youtube-dl written in wxPython.
DVDVideoSoft YouTube to MP3 Converter - Best YouTube to MP3 Converter of 2019. Any format, any quality, ad-free. Easy YouTube playlists downloads. Loved by users since 2006.
Youtube Video and Audio Downloader - Download YouTube videos in all available formats and extract the original audio files.
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!