CrossOver is an environment/Windows emulator of sorts, based on WINE. It’s not a full Virtual Machine (VM) environment and it’s not quite a emulator. It allows you to run Windows software without the need for a Windows OS, and it does so seamlessly within Mac OS X.

10.0.3 is mainly minor improvements, including areas dealing with upgrading/installing applications, and upgrading from an older version of CrossOver

Straight from the changelog:
* Fixed an installation issue with Project 2007 which produced a ‘Not installed for the Current User’ error message.
* Updated several built-in CrossTies. (These upgrades have been available online for a while.)
* Improved the MojoSetup (.bin installer) upgrade path.
* Added a progress dialog during initial open of a CrossTie on the Mac.
* Added support for the ‘installer’ keyword which supports CrossTies for stand-alone executables.
* Added RAR support to CrossTie installation.
* Added a ‘recreate’ button to the menus control panel.
* Fixed some menu issues on the upgrade path from CrossOver 9.2.

Download/Update
* If you have CrossOver, you can go into the help menu and “Check for Updates…”
* New users: Trial Download/Update
* Existing users: My Downloads page

Other than some font rendering problems (due to the install script) and some page lockups, they report it runs quite fast (note: this is running on an Intel-based Mac)