@ye No alts on other instances, but I do follow a lot of folks off-instances. I've personally gravitated towards hackers.town and infosec.exchange. I also periodically find interesting conversations being surfaced on retro.social.
If you like art/photography, there's good stuff on mstdn.tokyocameraclub.com, photog.social, and of course mastodon.art.
I actually recently followed a bunch more folks on refactorcamp.org, as I was becoming embarrassed that most of my interactions were off-instance.
Mastodon instance for attendees of Refactor Camp, and members of various online/offline groups that have grown out of it. Related local groups with varying levels of activity exist in the Bay Area, New York, Chicago, and Austin.
Kinda/sorta sponsored by the Ribbonfarm Blogamatic Universe.
If you already know a few people in this neck of the woods, try and pick a handle they'll recognize when you sign up. Please note that the registration confirmation email may end up in your spam folder, so check there. It should come from administrator Zach Faddis.