If you own the copyright over your GPL'd code, you can do a multi-license business model and sell/build proprietary stuff on top of the open core. (Or open stuf

If you own the copyright over your GPL'd code, you can do a multi-license business model and sell/build proprietary stuff on top of the open core. (Or open stuff on a proprietary core, or a mixed core, etc.) When other people do the same thing, suddenly you have even more open cores out there (besides the ones done without profit motive) to build stuff on that you'd otherwise have to reinvent at a negative cost factor. Mixing open and proprietary, while perhaps not in line with RMS's views, is still a great way to make money, and you can even do it with the GPL in many circumstances. (Not always though.) In the gaming industry, I find philosophically pleasing the approach of Carmack and some indie companies who make a credible commitment to open sourcing the software (not necessarily the art assets) at a certain date in the future while making money on it at release. Edit: I also want to add that copycat fears are generally out of proportion. Copycats usually don't win, as in displace the original's dominance. (What usually happens though is the original starts copycatting others to keep a safe, steady income flow, and possibly to crush newcomers if the thing being copycatted isn't sufficiently novel. You're not going to get big by copycatting, though you might get a modest sustaining profit.)