Hangfire and Oban are two other background job systems which have a commercial aspect. AFAIK Hangfire has been around almost as long as Sidekiq and is still actively supported.

I'm closer to $10m than $1m in annual revenue now.

My take on Sidekiq's secret sauce: a job system is a distributed system. Most of Sidekiq's commercial features are available as OSS gems but the complexity sneaks up on you as you integrate 3-6 of those features together. Building your own almost always leads to a worse system than the mature, well-debugged system which I have curated.