Original: CrossOver is a proprietary solution based on the open source Wine project that supports running Windows versions of Microsoft Office, Intuit applications such as Quicken and QuickBooks, Adobe Photoshop versions through CS2, and many popular games such as World of Warcraft and Team Fortress 2.
Simplified: CrossOver is a proprietary solution based on the open source Wine project that supports running older Windows versions of Microsoft Office and Adobe Photoshop versions until CS2.