Consider Phlebas (Culture, #1)

by Iain M. Banks

The Aoish were a banker species, and the credits were their greatest invention. They were just about the only universally acceptable medium of exchange in existence, and each one entitled the holder to convert a coin into either a given weight of any stable element, an area on a free Orbital, or a computer of a given speed and capacity. The Aoish guaranteed the conversion and never defaulted, and although the rate of exchange could sometimes vary to a greater extent than was officially allowed for—as it had during the Idiran-Culture war—on the whole the real and theoretical value of the currency remained predictable enough for it to be a safe, secure hedge against uncertain times, rather than a speculator’s dream. Rumor—as ever, contrary enough to be suspiciously believable—had it that the group in the galaxy which possessed the greatest hoard of the coins was the Culture; the most militantly unmoneyed society on the civilized scene. Horza didn’t really believe that rumor either, though; in fact he thought that it was just the sort of rumor the Culture would spread about itself.