CodeIgniter is a mature framework for PHP web applications. It's modularized and comperatively lean, requires litte configuration, comes with extensive documentation. CodeIgniter supports Active Record, Web-MVC, comes with security filters, autorization and persistence, localization, caching, loggin, standard URL routing, does not impose a templating engine, and works with almost any database.
major feature: CodeIgniter has been relicensed with the MIT License. CodeIgniter now requires PHP 5.2.4 and recommends PHP 5.4+ or newer to be used. The database drivers have had extensive refactoring. PDO is fully functional with subdrivers. There is a new Session library. There is a new Encryption library. The unit testing has been beefed up, and code coverage improved.