By using a single PHP file, that takes thew category Id/title from the URL. E.g. (note - not suitable for use in a production website, inout filtering omitted for sake of example)
PHP Code:
$cat_id = $_GET['ID'];
$c = new Category();
$cat_data = $c->get_category_info($cat_id);
$cat_products = $c->get_products_in_category($cat_id);
echo '<title>Products in: ' . $cat_data['Category_Name'] . '</title>';
//some more meta info maybe ....
echo '<h1>' . $cat_data['Category_Name'] . '</h1>';
echo $cat_products;
//do other stuff, cache results etc.