Yout - YouTube to Mp3 Converter
Savemp3.cc - An online free YouTube converter which allows you to convert videos and audios to MP4, MP3, M4A from YouTube, Facebook, Instagram, MixCloud, Dailymotion, VEVO, bilibili, niconico, etc. Supports HD MP4, 720p, 1080p video and 320kbps MP3.
Softorino YouTube Converter - Download YouTube video & audio. Watch and listen offline
y2mate.tv - Y2Mate YouTube Converter is not just a video converter, but also an audio converter. You can easily convert YouTube videos to the format you want, such as MP4 (320p, 480p, 720, HD 1080p), 320kbps MP3, M4A, WEBM, etc.
You-Get - Command-line utility to download media contents from the web
Zene Download - Zene is the new app that helps users find free music on Youtube, convert it to mp3 format and download for offline listening. Site is originally in Hungarian language, with English version included