These are not really post apocalyptic, or we have a different definition of an apocalypse. They are just federated, and work offline, but it assumes you still have electricity and access to modern hardware.

More post apocalyptic solutions existed for ages, my "favorite" is Collapse OS: It assumes all supply chains of hardware manufacturing will disappear, so we have to build with what we have: https://collapseos.org/

Unsure about offline-first, but yes, local-first, for which a LAN is enough and no cloud is needed, is very much what I'd rather we depended on more, instead of what's considered professional and an industry standard. Organizations requiring SaaS (as in, a network of 20 computers simultaneously becoming unable to open an app because the Internet went down) in a country experiencing war and blackouts is an additional source of stress. Free software requiring containers and gigabytes of dependencies is also suboptimal, we should aim to simplify native packaging for GNU/Linux and BSD distributions.

Another thing, programmer visions of what would suffice in bad situations are often very Western, anglophone. Software, including operating systems, eschewing localization in a quest for a lightweight footprint are not accessible or are outright unusable for the majority of the people in the world. Please take care to make your software possible to translate, including documentation. Best if the focus is on tutorials and handbooks; manpages are less of a priority.