A wiki with strong moderation tools, and gnupg signed/verified text built into it from the start.

An activitypub method to keep git repos in sync automatically.

A small blog type tool that's used as a replacement for facebook. It would have a hosted "gathering" component that is always online, then when you open your local app, it pulls down all your stuff.

Shared secrets like a distributed KeePass or Bitwarden.

Distributed home directory and/or development environments.

Something like the useful bits from KeyBase. I really wanted keybase to be something that could support this use case: Alice@foo gets a dev job at Bar. Her ID is added to the cool_project@bar group and automatically she has access to all the group's big bug tracking, file shares, wiki, git repos, group chats, etc. Her joining the group is recorded in a permanent record, which can be publicly or privately annotated by people specifically allowed by the group she joined. It'd become an automatic resume.