A collaborative task management system would be nice - the goals and tasks connected to POD files - with the access privilege functionality provided by Solid this would be easy to implement…
A general knowledge mangagement system usable for individuals, groups and business.
You can manage all assets related to specific tasks and goals and you can formulate business rules, logic and pipelines.
Should automatically create reusable middleware components (node.js is great for this).
Memex like applications/UI: this is a suggestion for UI and functionality along the lines of the Memex example below - the README has some nice gifs which show the UI in action.
This could be applied to Solid pods as well as for searching browser history as here.
This implementation stores data locally with optional backup to a server, so it might integrate well with Solid, and could provide a unified UI for search, tagging and annotation across local data, browser history, and pod, with everything you create stored in your pod.
The website has more animated GIFs showing the features and UI:
A kanban system, like Trello, but of the variety that also function as an an org-mode outliner.
I just heard a suggestion for a password manager that stores your (encrypted) passwords on Solid.