The Funkwhale music platform is alive and in active development, and they’re working on a feature to filter far-right artists off the network. Some Fediverse self-hosters are divided on letting a third party decide what should be allowed in their library.
I wouldn’t get too depressed about it, it would just be another niche bit of alt-tech if it were anything other than completely neutral. I can’t think of a case when an anti-left fork of a software was memorable as a self-hostable tool. The closest I can think of is Gab, which hardly qualifies, nor does it hold a torch to Mastodon.
Technically, SoapBox and Rebased were forks of the Mastodon frontend and Pleroma backend by an alt-right dev that found some level of success in the alt-right part of the Fediverse. So, it’s not completely unheard of.