England's Circe Cycles offers two brilliant tandems that convert to cargo bikes. The single most brilliant bit is probably that the second rider (the stoker) can range from about age 4 through adulthood. Bike families with teens know this will save a lot of money over the years, replacing several bikes liable to being outgrown. Riding solo or with a toddler or infant (or both)? Fit a huge rack and it's a cargo bike.