Alternative Number System: The eldrae, and thus the Empire, use base 12 – mostly because the common numeric base was agreed on by the same collective of the philosophically inclined that standardized the language, and they saw no particularly good reason why you should pick a number base just because that’s how many fingers you have when you can pick one based on something more useful, like its plethora of convenient factors.
There was a brief flirtation with base 16 (the Great Hexadecimal Reform) during the reign of the Online Emperor, but despite being more convenient for computational purposes (a base 16 digit converts into a whole number of bits, which a base 12 digit does not), it proved quite unpopular with the public and was later quietly dropped.
And, of course, other species have been known to use quite a large variety of numeric bases – 8, 10, and 16 being probably the most popular, but others far from unknown. Base 16 is commonly used for interspecies communication (outside the Empire, in the Worlds), though, mostly because everyone who uses computers is at least somewhat comfortable with power-of-two bases.
Except for those civilizations where ternary logic won out over binary, I’d imagine.