One of my favorite clients is a long standing newspaper of over 35 years. They have been through numerous content management systems and suffer from all of the bloat of that comes with exporting and importing into new systems. Category wise, there are a few hundred, many of them with the same name. The long term solution is to fix the problem by merging categories, trashing old ones. Until then, the editorial staff needed a quick fix to make their day to day lives easier. They wanted an additional tab that shows their categories in addition to All Categories and Most Used. This is a complete plugin that handled the issue. You must modify it to fit your own needs.