multicatalog is a basic Product Catalog Extension which is designed to be very easily extended and customized to fit a variety of needs.
Easy Extensibility works rocksolid and is documented within the code. The manual is work-in-progress.
At the moment Version 0.6 is in development which makes the catalog more feature complete and will be the first version which will be documented properly.
The next step will be the transition to Extbase for Version 0.7. Some initial work for this has already been done.