The "2.6 Beta 5" version specifically is notable because it bridges the gap between the older Windows 7/Office 2010 era and the more secure Windows 8.1/Office 2013 era.
Note: Because this tool is often flagged as a "hack tool," standard antivirus software will quarantine it immediately. Use in a virtual machine environment only. Microsoft Toolkit 2.6 Beta 5 Windows And Office Activator