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 a free and open source portable VNC viewer that provides secure remote desktop access without requiring installation. This lightweight remote control utility allows you to connect to and manage remote computers using your local mouse and keyboard, making it ideal for IT support, system administration, and troubleshooting directly from a USB flash drive.
RealVNC offers a free edition of its popular VNC viewer client software that can be stored and launched from a USB device. Virtual Network Computing (VNC) enables users to remotely view and control computers running a compatible VNC server. This stand alone remote desktop client provides encrypted access to remote machines from virtually anywhere, making it a convenient solution for personal remote access and on the go support.