Ignoring the really big open source players (Eclipse, Apache, Tomcat, Linux itself, GNOME, GIMP, etc), why is there open source? Partially because we finally figured out that if we all scratch our most pressing itch and share it with everyone else, we'll all be less itchy. It's less trouble to trade itch-satisfying code for nothing on the honor system than for every itch-filled developer to bother creating a shareware shingle and hope people shell out $20 to use those tools we've created mainly for ourselves in our spare time.