Bioreactors have been an important tool to study physiological behaviors of microorganisms. In recent years, rapid development in microprocessors, controlling unit, sensors, and software has enabled construction of reactors with more versatile functions, better performance, easier controls, and much lower prices. In our lab we have been developing our customized reactors since many years, which are based on Raspberry Pi microprocessor as the monitoring and controlling unit and syringe pumps as the pump unit. Such reactors have been successfully used in cultivation of "Candidatus Kuenenia stuttgartiensis" (an anaerobic ammonia oxidizing bacterium), Dehalococcoides mccartyi (an organohalide respiring anaerobe), and a nitric-oxide reducing Paracoccus strain. The reactor script was written in python and relied solely on open-source software packages. Online monitoring and data storage are achieved. Electronic lab book and git-powered script update are implemented. We believe that such reactor designs represent the future trend that calls for bioreactors with flexible functions and fully digital management at affordable prices.