In a series of books by David Brin [0] there is a galaxy-wide institution known as the library, and civilizations regularly mine its millions of years of data for suddenly-relevant-again techniques and technologies.
I remember one bit where a species had launched some tricky fleet-destroying weapon to surprise their enemies with esoteric physics, only to have it reversed against them, possibly because the Librarian that once helped their research-agent wasn't entirely unbiased.