The best replacement for categories is tags.

The best alternatives to categories are rated as following:
★★★★★  tags
★★  pages wordpress
★★  dimensions
★  categories
★  subclassing
★  folders outlook
★  folders
★  tags wordpress seo
★  labels gmail
★  class extensions
★  categoriessb
★  tags wordpress
★  custom post types
  sections
  keywords
  lists
  forums
  concepts
  tags blogs
  types
  functional categories
  sub categories

Your alternative for categories is not listed? Suggest!
Speaking about categories, one probably shouldn't forget about springboard.

Other search terms related to categories and their ratings are:
★★★★★ springboard
You have in mind a companion for categories and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of categories in all years. Click on graph for more.
categories
tags
pages wordpress