There's this composer named Eric Whitacre, and he does these videos called Eric Whitacre's Virtual Choir. It sounds cheesy, but the most current one he did was a collaboration between over five thousand singers from over one hundred countries. I think it's pretty impressive that the technology to which we have become so accustomed has made such things possible!
So yeah, the animation's really bad, but I don't care because it's really neat and you can see all the people who contributed!