resortquestioncategory - allows to resort categories alphabeticaly
renumberquestioncategory - adds hierarchical numbering to category names
quickrenamequestioncategories - allows to change names of all categories in one form
purgequestioncategory - allows to remove question category with all subcategories and questions.
plugins are placed into /local directory
Some possible use cases.
If you import into moodle large test bank with many categories they are sorted alphabeticaly and not by order in import file. Istead of long moving them up and down (with page reload on ever move) you may: a) manually add numbers to categories with quick rename; b) resort category with resort; c) remove numbers with renumber.
You may need purge if you imported complex question bank and suddenly found that something has gone wrong. Sometimes it's much simplier to fully delete imported category and reimport it.
I'll be happy to hear any comments and suggestions