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.
UltraVNC Viewer is an Open Source Portable VNC Viewer. This Virtual Network Computing or (VNC) application works as remote PC access software. The tool lets you administer remote computers using your local mouse and keyboard. This lightweight, no-install VNC client is perfect for IT support, secure remote access, and managing multiple systems from a USB stick.
RealVNC offers a free edition of their popular portable VNC viewer or client software 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. It works to provide secure desktop access to remote computers from anywhere.