I don't know if a list exists. Pinboard is profitable and I'm the only 'founder'. I believe Tarsnap (cperciva) is a one-man show. And the bingo card guy who posts here a lot runs things alone.
Some of those "single" founders have other support, like family and spouses - a local guy that's profitable leans heavily on his wife, who left her job for the company, so she should be counted as a "cofounder" :)
