The Choir of Cheahs (ie, one guy named Cheah, recording himself singing all the parts, and then mixing them together) performs the 40-part motet by Thomas Tallis, “Spem in Alium”. (Via the Recovering Choir Director.)
The story goes that the original performance idea was that the choir of 40 (or rather, the 8 choirs of 5 parts each) stood upstairs circling a room to sing the piece, and the listeners stood below in the middle. In this recording, we miss the beautiful interplay of voices against the ceiling and the floor and the listeners, and one cannot turn in a circle and experience the change in stereo. Also, you miss the rainbow of vocal colors provided by a choir of more than one guy, although the vocal blend is perfect. 
But that said, it’s incredibly awesome. Take a listen!
It was not unusual at that time to have small choirs in which every person was the only representative of his or her part. Knowing how to sightread and sing one’s own part was a fairly common accomplishment, and there were a lot of choral exercises designed to build confidence in singers so that they could go it alone. But a lot of modern choirs can’t or don’t do this; and of course, having twelve zillion parts is more effective if you’re playing with polyphony.
The text is rather interesting, when you consider that it is delivered by 40 people — “Hope in any other I have never put than in you, Lord God”. Forty is a symbolic number, too. Overall, it’s a penitent piece, but an overwhelmingly hopeful one.
