Steemit
Lemmy
Raddle
Tildes
Metafilter
Lancebase
Folkd
Pythonic news
Echo js
Littr.me
20-things
Lobste.rs
Hackaday
Southgate amateur radio news
Soylent news
Kottke.org
Federated thingies like Mastodon
(Drum roll please...)
Facebook groups
Twitter lists
Email lists
(If you're into art, be sure to check out art and artist groups/pages. People wonder where Flickr went and it's right there, not Instagram.)
Keep in mind that some of these groups actively use their Files and Photos sections which can be like gold.
FB's participation model does incentivize things like simple brigading & passive-aggressive behavior, though (IMO), so it's also a good idea to get a feel for the quality of discourse and moderation before diving in if you are interested in participating rather than lurking.
It's really too bad the participation model has to be so static across the entire platform, because some of the groups are one or two customizations/tweaks away from being really epic with regard to community particpation. You could solve a lot of the social problems there with a more dynamic approach to the software design & provisioning.
I mainly stick to HN, Lobste.rs, and a few tech related Reddits.
Thanks