This template strips categories from wikitext. For example, if passed the code "foo[[Category:Some category]]", it will return only "foo". It can be used to strip categories from templates as well; if passed the code "{{my template}}", it will return the template output minus the categories.
The template properly handles categories escaped with the colon trick, categories whose names include invalid characters such as ">", and categories that are surrounded with nowiki tags. However, it does not support complex wikitext such as nested links or magic words like __TOC__. Even so, it should still remove the vast majority of categories from any given wikitext.