MultiVNC is a cross platform multicast enabled portable VNC viewer. It can be used for stand alone VNC (Virtual Network Computing) to remotely connect to VNC Servers allowing you to access and share remote desktops on platforms that are running Windows, Linux, Unix, or Mac OS X.
RealVNC offers a free edition of their popular portable VNC viewer that can be stored and run from a USB device. Virtual Network Computing enables a user to remotely control any machine that is running a VNC Server.