There is a lib-taskman project on the google code hosting where you can find the full documentation, sources and latest releases. It's probably not that elegant as rake but if you want to stick to PHP and have Ant-alike functionality without any XML programming then taskman may turn out to be handy. taskman is very simple to use, it requires only one include, all its code resides in one PHP file, and it has no external dependencies.
He includes a basic use example that sets up the build with "task_hello", "task_comma", "task_world" and "task_say" methods that each do some basic output to show the flow of the process. He also gives examples of possible uses for the tasks like database bootstrapping, auto-code generation, project deployment, etc. He also mentions two other PHP-based projects that do similar things - pake and Phake.