Most of "multi-platform" CI tools I've seen are in the Java/.NET world, like TeamCity or Hudson. Is there a continuous integration tool that can handle both PHP and Rails projects?
Hudson is written in Java and is definitely Java-oriented, but it is sufficiently flexible to be useful in most environments. I've used it for .Net, raw C++, Qt projects with no problems. The general rule is that if it can be scripted then Hudson can do it.
There is addons for CruiseControl for Ruby and PHP:
and Atlassian Bamboo can handle both too (but is not free):
CruiseControl with phpUnderControl perfectly works together and do handles PHP projects but haven't tried using it with Rails.
It can do automatic uni tests, code analysis, and even auto deployment of projects.
http://topecoders.blogspot.com/2010/04/how-to-install-cruisecontrol.html
Instead of installing of your own platform you can use on-demand CI environment, like fazend.com. It supports both RoR and PHP. Everything will depend on your build automation software.