NASA has built many mechanical satelites and is in charge of most of them. They built the original GPS for the military, but have since then used it for every person. They also built satelites for weather and other such purposes.
The Moon is a well known satelite as it is the only one to revolve around the earth. This may not be surprising on the surface, however this is not the case. Most planets have over three moons or other satelites orbiting it, but for us this is not the case.