Matchbox is a modular system, which means you can group your controllers, models and views for a specific section of the site together. There's a new competitor called Modular Separation. Modular Separation is purely PHP 5 which gives it a slight edge over Matchbox from the get-go as it can leave out a lot of the extra PHP 4 support and go right for the much cleaner & quicker full OOP approach. It also includes 404 routing.

Popular CodeIgniter PyroCMS has now been converted to use Modular Separation and it has shaved a few 100ths of a second off here and there. I am not suggestion you drop Matchbox right now, but give it a try if you are starting a new project.

Check out the thread in the CodeIgniter forums here: http://forum.codeigniter.com/printthread.php?tid=31788