Economic model for impact of open source software

At first glance,thecompetitionbetweenopen-sourcesoftwareproductsandproprietarysoftwareproductsseems puzzling. Simpleanalogiesto othersortsof products,suchasconsumergoods(e.g. microwave ovens),are counter -intuitive. On onehand,it is unclearhow onecansuccessfullydemanda price for somethingwhich is beinggivenaway freely. On theotherhand,it doesnot appearto besustainableto make open-sourceproducts freely available.