The Sample is a newsletter recommender system I launched back in February (Show HN[1]). Last month we hit the milestone of 10,000 new subscriptions for other newsletters (at a rate of ~600 per week). It's making about $800/month currently which I'm thrilled about. Still a long way to go of course.
Next up, we're going to dig into our retention data and try to figure out if it's 'good enough'/what to do about it if not etc. I'm a little concerned about this since our monthly churn is 8% which feels pretty high, though I haven't compared it to benchmarks for other newsletters yet.