I started
https://netin.co about 9 months ago and now we have several customers including a government client. I live in SF so that's to say I need additional sources of income. I have another website which is pretty much an archive of a radio program that has been going for 10 years and that is a pretty good compliment to my income.
The growth curve for NetIn is rather smooth, I did the usual marketing for it, including creating a Chrome Ext, posting to LinkedIn, FB, Twitter, etc. I'd say the biggest difference came when I manually submitted a sitemap to Google with near 30 million URLs. Also after getting a lot of angry emails from people decided to remove all public info until a time when I can address the privacy concerns in a better way.
It's Stripe with monthly subscriptions, I tried calling prospects but soon realized I'm not a sales person, so now it's fully automated, it's free trial and then you pay if still interested in using it, no sales calls, no sales emails.