Clockwork automata on the micro-scale.
An article in the New Journal of Physics this month postulates a novel use for the not-yet-extant technology of nanotechnology: Building clockwork computers on a microscopic scale. The idea is that electronic circuitry isn't suitable for some environments but difference engines constructed on a microscopic scale might be because they would be far more precisely engineered and constructed with more durable materials. Sure, they'd be slower than conventional integrated circuits, but for some applications (like monitoring engine timings) you don't need a processor that can play Doom 3.
I hate to break it to them, but this isn't a new idea at all - Charles Stross beat them to it by a couple of years in the novel Accelerando. In the book, the IRS used nanoscale difference engines for security purposes because electromagnetic eavesdropping had advanced to the point where anti-TEMPEST technology was no longer effective. Still, I have to hand it to them - it's a technology that hasn't been explored in a serious manner in decades, and sometimes great advances can be made by re-implementing old developments. Also, if anything could spur development of practical nanotech (wet or dry), it's the prospect of new and interesting number crunching apparatus.