No Elxis does not support sub-categories yet, although in version 2006.4, we already made a small step to this direction (object now supports parent categories). Sub-Categories is a really useful feature but we did nt have the time to implement it yet. Elxis development done (and still based) on just two (2) people! We expecting people from the community to join us in order to spead up the development. This period we create sub-applications for Elxis so the main development has been frozen. Why? Because users continiously ask for free software. As for the difficulty: Subcategories is a very complex feature and not simple.