Copyleft - the Economics of Linux and other Open Source Software.

We build a model where the occupational choice of programmers determines the quality of programs in the consumer market. A monopolist, supplying the consumer market, has to take into account the impact the free software has on the market. When software implementation costs are low the monopolist will accept the presence of the copyleft program in the market. Our model explains the simultaneous presence of commercial and free copylefted programs in the market and laso why ther may not exist cimmercial alternatives to copyleft programs.