Hellenica is an encyclopedia of Greek culture, from classical Hellas, through the Byzantine Empire until the modern day, though its focus is on antiquity and especially the science and technology of Ancient Greece. Featuring technical diagrams and explications, there's no better site if you seek information on gigantic galleys, now obscure great Greek mathematicians, the last still working Ancient lighthouse and gears and how they were used by Archimedes and other ancients. This is not to denigrate other sections of the site, such as the page on the Olympics (including a Google Map of the site of the games), biographies of ancient, Byzantine and modern Greeks, the warring and healing of the Byzantines or the overview of Greek literature, taking in antiquity, the medieval era and modern times. That said, Hellenica is at its finest when treating science and technology.
A long list of links related to all aspects of the history of scientific instruments, such as sundials, slide rules, and pocket compasses.