2.1 Changelog:

* storyline texts for UFOpedia
* some new maps
** industrial, estate, bridge and oriental
* some new weapons
** micro shotgun, machine pistol, plasma blade
* a lot of new models, sounds and music tracks
* multiplayer
** heavily improved multiplayer support
** masterserver
* a hole bunch of bugfixes
* improved the engine to make it more stable and portable
* basemanagement
** implemented alien containment
** implemented base transfers
** finally implemented the hospital

For a full list see http://ufoai.ninex.info/wiki/index.php/Changelog/2.1