From Wikipedia:
Postcardware, also called just cardware, is a style of software distribution similar to shareware, distributed by the author on the condition that users send the author a postcard. (...) Like other "novelty" software distribution terms, it is often not strictly enforced.
The concept was first used by Aaron Giles, author of JPEGView.
What other things do you consider that could be paid with a postcard?


