A service site.

This is what i need. I need a webbsite that works almoset like google allerts. User-case is User visites the site. becomes member. writes down what they want to keep track of in the specific site. And How many days. And then they get an email as soon as a updates is made in the site that we want to bee watched. We need you to build a site watcher also, like a real time parsers as we say. You can do a google mushup if you like. contact for more info.