Where is the support for SEO friendly urls without mod_rewrite?
Your autoload function can be improved greatly....looping through each folder for classes could create quit a bit of strain if your framework becomes large and hundreds of classes start to autoload.
I see you are following the MVC architecture, but I don't understand how the index.php says put your code here, within a framework the index file should work as a initial load file and send requests loading the correct controllers, you shouldn't need to run the application from separate files. You are limiting the development by restricting the naming of views based on the action.
You have something started by there is room for much improvement.