"Notes and Domino is a cross-platform, distributed document-oriented NoSQL database and messaging framework and rapid application development environment that includes pre-built applications like email, calendar, etc." [0]

Lotus Notes was the original offline-first everything app, including cutting edge PKI and encryption. It worked over dial-up and needed only a handful of MBs of memory (before the Java rewrite at least). Has anything else really come close since?

[0] https://en.wikipedia.org/wiki/HCL_Notes