Ask HN: What are the different ways to achieve passive income?

Hi,

I'm Sunil. I work as a software developer in a startup. I love coding and building new tools that solve everyday problems. Over the years I've built many small tools, but none of them were up to mark to generate passive income out of them.

I would like to know about different ways using which I can generate passive income(>1K $ per month) on the side by using my computer. Ideas need not be only related to coding.

If you're already earning > 1K $ per month, a small story of how to achieved this would be helpful too!