As far as I know the word for base-three numbers is "ternary." It can also refer to mixtures/solutions of three substances which, like metal alloys, can have different properties from the individual components.

For the number-system usage see, for example, http://ips.ifmo.ru/en/course1/chapter1/lesson1/.

http://kosmoi.com/Science/Mathematics/Number/ also looks like a place to do some nice browsing, in other fields too.