Postage meters first appeared experimentally at the end of the 19th century and came into general use worldwide starting in the 1920s. By the 1960s more mail was being franked by postage meter than with traditional adhesive stamps. The trend continues today as mechanical postage meters are displaced by newer and more versatile digital franking machines and systems.
I use The International Postage Meter Stamps Catalog, written and published by Joel Hawkins and Rick Stambaugh for my literature.
My collection organizes and categorizes the stamps by their appearance (design format) rather than the meter model that printed them, as catalog is.