Similar questions the same site. Sometimes it happens that I've a problem (when I'm programming in Fortran, or when I'm writing a LaTeX document, ...) that I cannot solve on my own, so I open Google and search for an answer; I enter complete sentences if it's evident to me that there surely exist an already asked-and-answered question, otherwise I just write what I think are keywords to my problem. In the latter case the search process is harder and sometimes it happens that I don't find anything useful, so I decide to post a question. Such a question can result to be strictly related to (even if not really a duplicate of) another question. This question could be merged to the existing one in order to add some detail and make it more visible on the web.
Same questions on different sites. The questions about cross-posting are so many, and they make clear that it is not evil tout court. In general, an assiduous TeX.SE user can be so able to use Vim that he could easly answer a Vi.SE question even if it's barely related to LaTeX. But maybe this user considers vi just a tool, so he can have no vi account and, in turn, cannot see the question. But this question has tags, maybe a LaTeX tag. This tag could be used to make the vi.SE question visible on TeX.SE. To make a real example, this question of mine has been answered on TeX.SE, but maybe it would have fit better to Vi.SE, wouldn't it?
- Wouldn't it be useful to make SE sites more related to each other than they are now? I mean, a tag can be used to link different sites.
- Wouldn't it be useful to develop a graphical platform to navigate from one site to the other in order to find an answer? I'm thinking about something like a graph with branches connecting node. I think SO would be a big node connecting many other (smaller) nodes.
- About how to do something like this, it comes to my mind a program which can be used to automatically build a dependency-map of a program (made up of sub-program and modules) exploiting the source codes.