I wrote another SO clone, not really a clone but it has many features from SO and a bunch of features that SO does not even have. It's also in php but has much higher minimum requirements than this one, but if you have or can install php 5.3.2 or newer, you can use it.
I has all the features that I see people requesting in this forum and more.
I hope you guys don't mind me posting a link to my own project, but we are all Open source developers, there is not really a competition and hopefully we are all part of the great Open Source movement instead of competitors.
Anyway, my program still in beta, but have a look for yourself at our support site, ask around, see if this is something that may suite your needs.
I am also answering all questions on that site and currently I'm the only developer.