I like this concept of “local-first software”.  This is a very comprehensive survey.

Foundational part of it are Conflict-free Replicated Data Types.  Can’t say I know a thing about the details, but they sound pretty good:

CRDTs emerged from academic computer science research in 2011. They are general-purpose data structures, like hash maps and lists, but the special thing about them is that they are multi-user from the ground up.

Just as packet switching was an enabling technology for the Internet and the web, or as capacitive touchscreens were an enabling technology for smartphones, so we think CRDTs may be the foundation for collaborative software that gives users full ownership of their data.