USB Advance is homebrew program that allows you to play PS2 games from a USB Hard Drive connected to the PS2.
The USB in a PS2 console is USB 1.1 and a bit slower than DVD speed, so movies stutter for some games, while others just dont work at all. Many fixes have been found over the years and compatibility lists made. Around 50% of PS2 games dont work. Many utilities have been made to help ease the use of a USB HDD for gaming.
USB Extreme is the original program and is only distributed by a retail disc, USB Advance is the freely distributed version online as an ELF (ps2 executable) file.
USB Extreme User Guide - The original user guide
SKSApps - A collection of downloads for HDD apps, patches and utilities
USBUtil 2.0 - The newest utility with built-in patching for known fixes, game management and other various uses.
USBA Strip - A utility to decrypt/unpack and re-skin USBAdvance