For anyone who's ever used jMock it will be instantly recognisable since the API is almost 100% taken from jMock (think of it as a jMock clone), but tailored to work well with PHP.
You'll need PHP 5.2 (EDIT | 5.1.2) or higher with the SPL extension to use it.
http://code.google.com/p/yaymock/ (will get a home on it's own website eventually)
This is the first release so any bugs should be posted on the Issue Tracker.
The Documentation is already pretty concise but I'll work on that more.
Differences from SimpleTest:
* Expectations based on method invocations not on timings
* The mock objects do not have any additional methods inside them (they really only have the mocked methods and no more)
* Expectations can be constrained to specific states
* PHP5 compliant
Current disadvantages over SimpleTest:
* The error messages are effectively a log dump of what happened, but do not describe parameters currently
* There is no partial mock support in this release
The outstanding issues will be addressed asap, but for now I just wish to get some people using it to pick up logic errors rather than features. I actually don't belive there are any bugs with this version since it's actually very simple the way it all works, but I'd like to address anything that does come to light before a non-beta release.
Feedback most welcome