- Mobiledoc - github.com/bustle/mobiledoc-kit - framework to build editors with a standardized JSON structure
- ShareDB - github.com/share/sharedb - framework to sync any JSON document using operational transforms, add real-time collaborative editing to anything else
- Bangle.dev - github.com/bangle-io/bangle.dev - toolkit built for building editors, based on prosemirror
These use separate document structures instead of HTML, some are more modular libraries than full editors