• Plug-In Registry (see the xmorph and guash plug-ins)
• Documentation
• On-line User Manual
• On-line Tutorials
• Developer's FAQ
• Writing a GIMP plug-in tutorial
• Annotated plug-in sample
• Script-Fu pages
• Script-Fu tutorial
• Scheme (also see question 39 of the Gimp FAQ)
• Gimp Batch Mode