Automated website analysis and regression testing suite

[thing2b]

This is a long shot, but can anyone here point me to an open source (PHP preferred) website regression testing suite. (To test that all previous website items still work)

What I am wanting to do is to have a pile of things checked every now and then. The problem is that I have many large websites and can not run checks all at one, so I need to do/spider/check a small number of pages at a time.

All the websites are under constant development and the testing suite is required to make sure that changes to not affect any current offerings.

The type of tests that I am wanting to run on every page are any of the following:
- 404 link checking
- Link destination page change (to tell me when a page I link to might have changed its content or detecting sites that do not ever serve 404s)
- Spelling and grammar checking (may as well just do it while we are at it)
- Page/HTML changes (tell me when HTML changes so that I can see if a recent programming change has resulted in the unexpected loss of a on-screen item)
- Download changes (for example checking that dynamically generated PDFs still work)
- HTML, RSS and other pages validate (and are accessible with Section 508 Web Accessibility Standards if applicable)
- I am not really looking to load test at the moment
- Track when tests run and hence include an uptime monitor
- Note down pages that are not well listed in search engines to be worked on latter (SEO'ed)

Can anyone make some suggestions?