Multiple databases

Through some kind of incompetence, I seem to have ended up after years 
of use with multiple monotone databases with the same name.  I don't 
even know if their histories are compatible or whether they have nothing 
at all to do with each  other.  Desiring to have only one (except for 
sync-style redundance), and that one being valid and up-to-date, I'm 
going to have to examine them to see what's in them, and how they 
differ.

What tools or practices would expedite this endeavour?

-- hendrik