RESTful.php

<?php

function RESTful($root, $convention = '_%s')
{
	$root = rtrim(str_replace('\\', '/', realpath($root)), '/');
	$segments = preg_replace('~/+~', '/', trim(substr($_SERVER['PHP_SELF'], strlen($_SERVER['SCRIPT_NAME'])), '/'));

	foreach (range(0, count($segments = explode('/', $segments))) as $i)
	{
		if (is_file(sprintf('%s/%s.php', $root, $path = implode('/', array_slice($segments, 0, $i)))) === true)
		{
			try
			{
				if (class_exists($class = sprintf($convention, basename($path, '.php')), false) !== true)
				{
					require(sprintf('%s/%s.php', $root, $path));
				}

				$method = new ReflectionMethod($class, strtolower($_SERVER['REQUEST_METHOD']));

				if (($method->isPublic() === true) && ($method->isStatic() === true))
				{
					if (count($arguments = array_slice($segments, $i)) < $method->getNumberOfRequiredParameters())
					{
						throw new Exception('Bad Request', 400);
					}

					exit($method->invokeArgs(null, $arguments));
				}
			}

			catch (ReflectionException $e)
			{
				throw new Exception('Method Not Allowed', 405);
			}
		}
	}

	if (count($segments) > 0)
	{
		throw new Exception('Not Found', 404);
	}

	return true;
}

StackOverflow.php

<?php

class _posts # /rest/posts.php
{
	public static function get($id, $action = null)
	{
		Dump(__METHOD__, func_get_args());
	}

	public static function post($id, $action = null)
	{
		Dump(__METHOD__, func_get_args());
	}
}

class _questions # /rest/questions.php
{
	public static function get($id = null, $slug = null)
	{
		Dump(__METHOD__, func_get_args());
	}
}

class _ask # /rest/questions/ask.php
{
	public static function get()
	{
		Dump(__METHOD__, func_get_args());
	}

	public static function post()
	{
		Dump(__METHOD__, func_get_args());
	}
}

You might like this micro router based on anonymous functions.

@xeoncross: That's pretty sweet. But it's still regex based...

I was hoping to address this: http://stackoverflow.com/q/14592181/89771.