One tsp. uses tags for organizing recipes, rather than a list of pre-defined categories.

You can add tags to any recipe from the options on the right-hand side of the recipe page. Then you can browse through all of your tags by clicking "recipes" from the top nav, followed by selecting "tags" from the tabs above your recipe list.

For ideas on how to make good use of tags to organize your recipes, read this blog article: Use tags to categorize your recipes.