I had heard of mastadon but since I was never really big into twitter, I ignored it. Also, I think the first article I read about it was on how to set up your own instance and invite friends to it and that seemed way more than I would want to do.
Reddit, on the other hand, was a big deal for me, and learning about lemmy and kbin was an eye-opener. I was on digg before reddit and was afraid whatever the new thing was would eventually suffer the same fate, but I’m cautiously optimistic the fediverse model may be more resistant to the corrupting influences? We’ll see I guess.