Try Dispatch: https://github.com/noodlehaus/dispatch
require 'dispatch.php';
get('/', function () {
echo "Hello world!\n";
});
dispatch();
It's a single-file routing framework for PHP. Very light-weight, very easy to work with. This one and Slim are my favorites.
I don't require a full-blown framework at all. If you need an ORM, try Redbean.
If you need a template engine use Twig.
With this approach you just install what you use.