Background from TechWeb,
http://www.techweb.com/encyclopedia/defineterm.jhtml?term=usb

USB - Universal Serial Bus

A hardware interface for low-speed peripherals such as the keyboard, mouse,
joystick, scanner, printer and telephony devices.  USB has a maximum bandwidth
of 12 Mbits/sec (equivalent to 1.5 Mbytes/sec), and up to 127 devices can be
attached.

USB ports began to appear on PCs in 1997.  It has now essentially replaced the
older RS-232 serial and Centronics-type parallel ports on modern PCs, and USB
has become the primary means for connecting most external devices to today's
computers.

The following project aims to provide USB compatibility to the Atari:

MicroUSB.org - Microprocessor USB Project, http://microusb.org/
Project USB Cartridge
    * Project Name  : USB Cartridge with two USB Slots
    * Project Start : Summer 2002
    * Project Member: Marc Brings, Thomas Grasel, Harry Reminder,
                      Guus Assmann, Carsten Strotmann
http://atariwiki.strotmann.de/xwiki/bin/view/MicroUSB//ProjUSBCart

In cooperation with the above,

Atarimax(Steven Tucker)/ABBUC USB Cartridge:
http://www.atarimax.com/usbcart/