Loopt, the first location sharing mobile app. I think the exit was around 40+ million is I remember correctly.

Here's more about it. http://venturebeat.com/2012/03/09/loopt-dau/

I just googled "Sam Altman" and among the top few links was the Wikipedia article:

http://en.wikipedia.org/wiki/Sam_Altman

I then read that and it answered your question plus extra. i recommend the same technique for most other topics. Very fast, self-serve, great for FAQ-prone facts.