I think this is an interesting idea, check it out!

Antipodean - PHP OO Programming reinvented

Author Dennis Hotson says about it:

There are some interesting implications of this:

• Classes can be hacked / patched / cloned. Methods can be added to classes at any time
• Classes can be scoped. They’re not global, unless you want them to be.
• Classes can be temporary (and garbage collected).

Although I don’t think it’s that useful or advisable, it’s a great example of how far you can push PHP’s limits.