[byoung2]

More recently, Omar Hamoui was a solo founder of AdMob, which sold to Google for $750 million

Andrew Mason was a solo founder of Groupon, started with $1 million seed money from a former employer.

[ethnomusicolog]

Do we all realize that Mark Z... is actually a single founder ?!

[byoung2]

That's up for debate. Zuckerberg did early hacking on his own, but he started the company with Dustin Moskovitz, Eduardo Saverin, and Chris Hughes.