I’ve gotten to know @jcrabapple@screengeeks.club because we’re both Mastodon instance admins and he has been super helpful. He just started a new server at https://screengeeks.club which, as the login page explains, is “A CalcKey instance for fans of movies, TV, video games, and tech!” It is relatively new but a fun idea.
Yup, it is built on ActivityPub and you can follow people between platforms if you wanted to. It is closer in experience to Mastodon in terms of microblogging feeds as opposed to forum posts like Lemmy. But, an interesting & modern interface. Personally, I still spend most of my time on Mastodon but I like to experiment with the different Fediverse implementations.