Workflows in cell and molecular biology often use microliter volumes and containers with solid walls (e.g., microcentrifuge tubes, microplates). An accessible technology that provides an easy entrée into the use of nanoliter volumes will be described. In this case, liquids are confined by fluid (not solid) walls. Aqueous circuits with any 2D shape, or grids containing thousands of identical chambers, are made in seconds using standard cell-growth media on polystyrene Petri dishes; then, interfacial forces pin liquids to substrates, and an immiscible overlay prevents evaporation. The confining fluid walls are pliant, resilient, and optically transparent; they self-heal when liquids are pipetted through them, and they can even drive flows through circuits without the need for external pumps. The technology will be illustrated using some common cell-based workflows (e.g., cell feeding, replating, cloning, cryopreservation, lysis plus RT-PCR, transfection plus genome-editing, fixation plus immuno-labeling, and the response of human cells to cytokines and drugs, worms to osmotic stress, and bacterial biofilms to chemotactic gradients).