Trello is a handy tool for keeping track of list items, but it limits you to a single row of lists. This lightweight, keep-it-simple extension for Trello allows you to create multiple horizontal "swimlanes" of lists.
Just add the swimmer emoji 🏊 or the pipe character | to the header of any list that should start a swimlane, and you're all set! The lane will be labeled with whatever text follows the swimmer, so if the header reads "Backlog for 🏊Project X", that lane's label will read "Project X".
Moving lists around can cause Trello to get confused and show everything in one lane again; just reload the page to fix it. You may also find it easier to toggle off the extension, re-arrange your lists, and then re-enable the extension. (This is not ideal, for certain, but it's so far unavoidable.)
Note: the extension may ask for permission to view your browsing history. This is to allow it to activate itself only on Trello pages; it is inactive anywhere else. It does not and will not collect, save, or transmit your browsing history.