RDP
From Sun Ray User Group Wiki
RDP is short for Remote Desktop Protocol. RDP is the built-in protocol to Windows (XP, Terminal Server, Vista) to allow remote administration and multi-user. The RDP Server runs on the Microsoft side and RDP clients access the server.
Sun provides a fully licensed RDP Client with the Sun Ray Connector for Windows as part of the Sun Ray Software 4 Suite.
Rdesktop is a popular open source RDP Client.
Sun Secure Global Desktop provide RDP access to MS Windows Platforms and shares the same code based as the Sun Ray Connector for Windows.

