- Hydrogen Audio for digital music library management: https://hydrogenaud.io/

- Gearslutz for music production and audio engineering: https://www.gearslutz.com/board/

- Head-Fi for headphones and portable players, amps, DACs, etc.: https://www.head-fi.org/forums/

- Not a forum, yet still a strong community: Discogs for music collectors: https://www.discogs.com