I generally like what's happening in the
Nostr sphere.
While Nostr is not a blockchain project itself, it is decentralized and uses a similar type of cryptography as Bitcoin to handle accounts and data. It was originally mainly used for microblogging but supports a lot of other social media use cases like decentralized marketplaces, so you can use it for all kinds of social interaction, including social trading.
It provides exactly what you write here:
Imagine a platform where you truly own your data, where your privacy is protected by default, and where you have control over how your information is used.
Value4Value is a project to combine Nostr with blockchain-based micropayments, for example via Lightning Network. A lot of podcasters and other content creators have begun to create an economy based on Nostr with the tools provided by this project, which of course is open source and free.
About on-chain social media and SocialFi projects I'm more skeptical. I have used occasionally Steem(it) in 2016/17 which was one of the first of those projects. But many projects suffer from centralization and scaling problems.