Metafilter https://metafilter.com still has interesting comments and occasionally unique content, besides the links which bubble up everywhere. It's pretty heavily politically left, which, along with heavy moderation has driven away a lot users over the years, but sometimes still has some nuggets you don't see on other aggregators. It is much more of a community than most of the other sites, with lots of rules and sub-sites, but I've only read the comments.

Twitter has been surprisingly useful since I started using last year. If you only follow accounts in a specific area of interest it really allows you to discover new things. The hard part is dealing with power poster/users since they can quickly dominate your feed, but they also can bring in new areas of interest. It's too bad they don't have better tagging curation tools.

Serializer https://serializer.io/ is a meta-aggregator which grabs stuff from HN, Ars, some Reddit forms and others, not sure if this counts or not.