http://www.codeigniter.com/
Changes compared to CodeIgniter 2:
The framework is released under the MIT license
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
PHP 5.4 or newer is recommended, but CI will still work on PHP 5.2.4
More: http://www.codeigniter.com/userguide3/changelog.html
终于,本来以为CI已被弃置不再维护…