They utilized an unknown alloy that was harder and lighter than any metal registered, Their construction techniques drew the alloy into filaments and were spun like a spider's web. Their architectural designs incorporated hexagonal cell formations that were nearly identical to the honeycombs of bees on Earth. Among their more unique technology utilized was the energy accumulating wands they used to collect energy from motion, sound, light, heat, and magnetism.
It is unknown how or when they became extinct. The only recorded trace of their existence is the hulk of a huge Pod Ship on the fringe of the Milky Way.
Source: Star Trek: The animated series: "Beyond the Farthest Star", Memory Alpha