Thinking about web apps I'd like to see, maybe they already exist, I've been pretty busy and pretty upset, so I haven't been keeping up as well as I might.
One thing I'm interested in is trying to generate metadata about arbitrary data sets by collecting rich information about the relations between objects in the data set. I guess I'm thinking about something like free tagging only applied to relations between objects rather than the objects themselves. Something like an extreme generalization of the 'Am I Hot or Not?' variety of site might be a fun way to do this. Allow users to submit arbitrary objects and some relations between them. If we're restricting ourselves to dyadic relations, users could be presented with object pairs and asked whether they relate in a given way, if the relation is such as to apply to the object pair in question at all, etc. If done properly, I'm pretty sure, the relation semantics could be enriched in a similar way with more complex scenarios designed to determine if relations are commutative, symmetrical, etc.
Another thing I'd like is a project/collaboration-oriented social network, I'm thinking a framework for proposing projects, collecting members & funding, providing communications & planning infrastructure, canned work flows for a variety of organizational structures, etc. This seems like an obvious thing to do & something worth doing, so it seems like somebody should've done it already, but I'm not aware of it. It may be just that design for project planning/management apps is still very oriented to the technical user. There might be something to learn from the proliferation of to do list type apps out there.
Anyway, as I say, I'm very busy & upset, could somebody put together mockups & get back to me?