Sidekiq by Mike Perham http://sidekiq.org/
Over 1MM annual revenue https://www.indiehackers.com/businesses/sidekiq
Over 1MM annual revenue https://www.indiehackers.com/businesses/sidekiq
As long as other open source contributors are not payed for their contributions, I would still qualify it as a single person company. It's just that the company's approach is a little bit different than the traditional one.