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.
ShowMyPC; A Free Portable VNC Server and Viewer all in one. This remote desktop sharing software allows for remote PC access, screen sharing, and remote support.
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.
TightVNC Portable is a popular open source free and portable VNC Viewer that can be stored and run from a USB flash drive. Virtual Network Computing or (VNC) enables a user to view the desktop of a remote machine and control it with a the mouse and keyboard from a local machine as if you were sitting right in front of the remote computer.