Passive income ideas !?

Can anyone suggest some passive income generating ideas that I can do along with my 9-5 job

Guys what are some cool ways to make passive income. Avenues which are non intuitive but profitable

Any ideas or thoughts we can earn some money working on weekend or post our office working hours? I think most of us already doing it. Appreciate if they throw some light.

Thanks!

I am certainly thinking about passive income...what would be a great idea to have a passive income for 9-5 job guys ( don't mention high investment businesses ).