Mike Perham's Sidekiq was what I modeled my own business, EmailEngine, after

Mike Perham's Sidekiq was what I modeled my own business, EmailEngine, after. I took my decade's worth of expertise in email protocol implementations (I also run the open-source Nodemailer library) and built an email gateway app my customers can download and run on their machines or servers. Just like Sidekiq Pro, the customers need an active subscription to run it, but the app runs on their premises, and they maintain it. I only run the key generation and validation server, which costs me around $50 per month, including all the backups and so on. I quit my job to go full in with EmailEngine exactly one year ago, when MRR for EmailEngine was $500, now it is $3,900 and steadily growing. I do work full time on it, but the result is async - the work I put into EmailEngine today brings me income sometime later, and the recurring income I receive today is unrelated to any effort I put into the company right now.