Looking for ideas on how to make money even while sleeping(brainstorm session)

I am looking for ideas on how to make money without doing anything. Something ideal for busy employees to maximize the power of their savings by making it earn more money passively. I am currently doing research on that. If you have any idea how mail me at juantipid@gmail.com. I'll be posting what I've researched when I've completed it but contributions are welcome. =)