For years people have pointed out the downsides of sites like Facebook, Twitter, and YouTube having content recommendation systems (CRSs) (news feeds, etc) built to optimize engagement (in order to optimize ad revenue). The interests of the companies don't align with the interests of the users leading to suboptimal recommendations from the perspective of users.

Do there yet exist any companies whose product is the CRS itself? Built to optimize the user's preference?

I'd like such a product, and would like to have several feeds that I can optimize for different types of content that I want to see at different times.

(In a way Reddit is *sort of* like this. Users can go to different subreddits to see different kinds of posts. But Reddit posts are all for the public--they don't include personalized posts for specific social circles like e.g. Facebook--and therefore Reddit only has a subset of the sort of posts I'd want to be includeable in my customized feeds.)

It would also be nice if I could make a feed that includes posts from more than one website, e.g. Twitter and Facebook posts appearing in the same feed.

Does anything like this exist yet?