Side hustles can be very fruitful! While not tech related, I side hustled with a friend into starting a specialty wet wipe manufacturing business that we ran for 4 years and sold. The side hustle phase was done on PTO and weekends. We worked with the machine maker to get samples that we took to restaurant/hospitality expos to gauge demand. We made a deal with the machine supplier to send finished goods until the machines arrived. Four years later we sold it and I went back to corporate life. It was worth 100x an MBA.