This addon is a plugin. You need to extract it to your /plugins folder to install it.
This add-on will hide all discussions that are set as a Sticky from the Discussions page. The discussion count is adjusted because of this. The Sticky will only be shown when you actually view the Category.
Thanks to WallPhone for his ideas.
After a question to see how you could add a Category Sticky to the index, I simplified the code after re-looking at WallPhone's and added a variable and explanation in the readme file to help you do this.