An IE script is a chunk of Javascript code. It is loaded when the web page you visit match the rules specified in the script, such as targeted domains, or a set of domains.The user script can modify the page by injecting elements in it, removing elements in it, or setting styles for it, or even more, directing the page to other site.
IEScripts does its best to be compitible with GreaseMonkey's user scripts, so the developers can port GreaseMonkey's user script easily to IEScripts. GreaseMonkey is a Mozilla/Firefox plugin support thousands of user scripts hosted in UserScripts.org.
In correspondance to userscripts.org, IEScripts.org are providing many scripts for Internet Explorer users.