From TightVNC Software:
TightVNC is a remote control package derived from VNC, with many new features, improvements, and bugfixes over the standard VNC version. It works well with slow network links such as modem connections, provides more configuration options in the server, includes improved Java viewer, and more. The modified servers and viewers are fully compatible with the original VNC software.
TightVNC Portable makes TightVNC keep its configuration and connection history in the installation directory (typically, on a USB flash drive), instead of using the registry of the host computer.