Have a saas I built for a large company to manage their marketing and advertising. Deployed about 8 years ago. Two employees, myself and my brother. Built it in php, and javascript and was the first web based app I had ever built. Got paid about 150k to build it and then we have been netting ~$2500 a month (we then split it 50/50) for the last 8 years. No upgrades or additional work done. Most months all I do is send in the invoice. Hardest part was remembering to renew the ssl cert each year. This month was the last month as the company has switched to a standard solution across all their departments. Was a good ride now I have to figure out something else to build. Worked a regular job this whole time as well.