are the most widely used models for GPL'd software. The GPL is

central to their success, because it ensures that the code base

remains common, and that large and small companies are on equal

footing for access to the technology. Consider, for example, the GNU

Compiler Collection (GCC). Cygnus Solutions, a company started in the

early 1990s, was able to grow steadily simply by providing services

for GCC --- mostly consisting of new ports of GCC to different or new,

embedded targets. Eventually, Cygnus was so successful that

it was purchased by Red Hat where it remains a profitable division.

However, there are very small companies that compete in

this space. Because the code-base is protected by the GPL, it creates and

demands industry trust. Companies can cooperate on the software and

improve it for everyone. Meanwhile, companies who rely on GCC for their

work are happy to pay for improvements, and for ports to new target

platforms. Nearly all the changes fold back into the standard

versions, and those forks that exist remain freely available.

\medskip

\label{Proprietary Relicensing}

A final common business model that is perhaps the most controversial is

proprietary relicensing of a GPL'd code base. This is only an option for

Some companies use this to their

financial advantage with regard to a GPL'd code base. The standard

version is available from the company under the terms of the GPL\@.

However, parties can purchase separate proprietary software licensing for

a fee.

This business model is at best problematic and at worst predatory because it means that the GPL'd code

base must be developed in a somewhat monolithic way, because volunteer

Free Software developers may be reluctant to assign their copyrights to

the company because it will not promise to always and forever license the

software as Free Software. Indeed, the company will surely use such code

contributions in proprietary versions licensed for fees.

\section{Ongoing Compliance}

GPL compliance is in fact a very simple matter --- much simpler than

typical proprietary software agreements and EULAs. Usually, the most

difficult hurdle is changing from a proprietary software mindset to one

that seeks to foster a community of sharing and mutual support. Certainly

complying with the GPL from a users' perspective gives substantially fewer

headaches than proprietary license compliance.

For those who go into the business of distributing {\em modified}