I stake and lend cryptocurrency (stablecoins and blue-chip coins) on lending protocols and exchanges, and am at around $500 a week.
Not really a side-project per-se, but I do quite a bit of calculation on ROI, where to move what share of my funds to, and occasional yield-farming strategies so it does take a up a good bit of time
The goal is to have that stable enough so that I can quit and focus on my actual side projects that I am hacking on after work