A copy of Windows Server only permits installation of the operating system on one computer. A server license by itself does not provide the legal right for others to connect to that computer, whether they work for the company or not. Instead, each user needs a Client Access License (CAL).
For each employee, or each employee device, that accesses the Windows Server installation a CAL is required, but not for anonymous users who access it over the Internet.
Server CALs are cost effective and affordable, allowing customers to pay only for the licensing they need with the option of buying more as their businesses grow.
Windows Server 2012 Standard
Windows Server 2012 Datacenter
Windows Server 2008 R2 Standard
Windows Server 2008 R2 Enterprise
Windows Server 2008 R2 Datacenter