Sidekiq makes ~1M/year in gross revenue. I believe the only full-time employee is the founder, and it doesn't sound like there are any material recurring expenses:
https://www.indiehackers.com/podcast/016-mike-perham-of-side...
It's the most profitable one-man show I know of, although there's many that I've run into that ~500k, albeit with a much higher operational burden.