A cross-platform chat program with high-quality audio chat capabilities. It also can call phone numbers and receive calls from regular telephones, though these services cost extra. Personally I prefer iChat, but a good friend of mine is in the Peace Corps, and Skype's audio chat works great over dial-up; iChat's, not so much.
Perhaps it somehow impregnated the sperm that would one day conceive Kahn's daughter, so that she'll be born pregnant, like that lizard who was not in any way, shape or form related to Godzilla.
Comments
http://skype.com/
Seriously though, I think you could have figured all this out via Google or Wikipedia or something.