SWI-Prolog is being used for commercial applications. The license conditions allow for embedding in commercial applications without restrictions on the license conditions for the proprietary code.

We welcome commercial usage of the system. Commercial users have had a major impact on the system by sponsoring the development. Examples of sponsored features and components are:

• The initial garbage collector
• Unbound integer and rational number support
• The PlDoc documentation system
• The PlUnit testing system
• The SSL interface
• Redesign of the (stack) memory management to avoid using the C stack for recursive traversal of Prolog terms, make threads more memory efficient and remove the limitation of the number of threads.

Commercial users have greatly helped in debugging several features, notably multi-threading support and the ODBC interface.

Finally, commercial users have provided packages. While making your package available requires an investment, you get a pay-back because others will help you to debug it and clean the interfaces. Examples of such packages are:

• The JPL Java interface.
• The TIPC networking interface.
• The Google protocol buffers interface.
• The CQL library

Involvement of commercial users is vital to the project!