I've started working on this test/monitoring tool. The initial idea was that I wanted to simulate having some visitors on the webpage I was working on. That is in the test environment, not available on the Internet.
Then I came accross a tool, SiteImprove, that helps editor find spelling errors, dead links, unwanted texts like "lorum ipsum"... so those use cases were also added.
It is an ongoing project. Implemented as a core, which is basically a crawler, and plugins that can listen to the core, or each other. There will be some plugins in the initial release, for HTML validation and spell checking for example. Any user can easily write his or her own plugins.
Check it out at GitHub =)