1. Selling domain names. This was when I was in college and somehow traded my way into mid-high five-figure domain names. I turned over $100k in profits in a year, and then 2008 happened and all markets collapsed.
2. Starting a D2C brand. Shipping is automated via a third-party provider. Sourcing is easy since I have a very reliable supplier. All marketing is through word of mouth. I get around 300 orders on Amazon monthly, some 100 on our website, and land the occassional business order that gets me around 2,000 orders extra per year. Not a huge money maker, but pays my mortgage for practically 2-3 hours of work/month.
3. I ran an informational website about music production (I produce as a hobby). Somehow, a few of my articles became popular and I landed a ton of good links. Google loved my website and I was pulling in mid four-figures in affiliate checks every month. That went on for years even when I stopped working on the site.