The RAPID Web Sync extension allows for automatic creation of categories in Magento directly from Sage 300 ERP and Sage ERP X3.  To use this feature, you must enable the “On the fly category creator/importer” Magmi plugin.  By default, a forward slash is used as the category delimiter, however you can configure this plugin to use a different character.  You can configure the plugin to add the product to each of the categories (if using multi-level categories) or to assign it only to the bottom-level category.

After creation, the name and description can then be permanently set within the Magento web admin by navigating to Catalog -> Manage Categories within the Magento admin panel.

For more information, please see the wiki page for this plugin: