Tried several plugins for collapsing categories and by far this one beat the others hands down. Gave it five stars. I wanted it to work in the WP built Categories and not as a separate Categories widget and it does. I was able to tweak the settings to match the other text in my template. I am using a template from the Themes directory, not the ones that came with WP. I am delighted with this plugin.
I do have one request. Mouseover gives the category name. The WP built in mouseover gave the category description so a person would know what it was about before actually clicking on it.
So my feature request is to have the mouseover popup give both the name and description (in case the name is longer than what is visible).