Postcardware, like other "novelty" software distribution terms, is often not strictly enforced.
The concept was first used by Aaron Giles, author of JPEGView. Another well-known piece of postcardware is the roguelike game Ancient Domains of Mystery, whose author collects postcards from around the world. Orbitron is distributed as postcardware. Exifer is a popular application among digital photographers that is postcardware. Caledos Automatic Wallpaper Changer is a "still alive" project cardware. Linux was postcardware for a long time as well.