Magmi is a mass importer for the Magento e-commerce system. It is most useful when you need to import a big product catalog into Magento, even one with several millions of articles. Moreover, it has many capabilities concerning input data manipulation and an open and flexible plugin model for adding new capabilities.
Information regarding Project Releases and Project Resources. Note that the information here is a quote from Freecode.com page, and the downloads themselves may not be hosted on OSDN.