You can think of Yjs as a protocol for data synchronization. It gives you a way to describe a JSON-like data structure (i.e. nested lists and maps), and keep them in sync across multiple devices.
Yjs itself doesn't provide a platform, but it's an open protocol so there there are service providers (like ourselves[1]) that offer Yjs backends as a service (other notable providers are TipTap/Hocusocus and Liveblocks).
The biggest difference is that Y-Sweet is built around object storage (i.e. S3 and friends) rather than a database.
This allows writes to scale horizontally without a central database being the bottleneck. It’s also a much cheaper way to store lots of documents accumulating over time on S3 than in a database. This is because compute scales with how much data you actually access, not how much data you store.
I wrote about why object storage is a good fit for this here: https://digest.browsertech.com/archive/browsertech-digest-fi....
what's the main differences in your opinion between y-sweet and Hocuspocus?