USB stands for Universal Serial Bus. See http://www.usb.org/ for information about USB.Tom Wilkason seems to be successful teaching Tcl to send data through USB ports , as was Uwe Klein, with a SWIGified libusb ...UK the google newslink leads me down a dark alley;-?. I've put a swig of my libusb effort on the net: http://home.foni.net/~kuttersegeln/swig_libusb-20050616.tgz
ToolsFlexiHub: is a utility which allows to share USB and Serial port over Ethernet, access and manage remote USB and COM port devices from everywhere. Available for Windows, Linux, Mac OS and AndroidUSB Network Gate: helps to share USB devices via Network (Internet/LAN/WAN) among multiple computers as if the device was plugged into your own machine. Available for Windows, Linux, Mac OS and AndroidUSB Analyzer: offers simple, yet complete view for monitoring and analyzing activity of USB devices.Jan Axelson: USB Development Tools
"Integrating USB into Products" 
AMG: http://www.dlpdesign.com/usb/usb245.shtml is an outstanding product. On my first project using it I had a supremely easy time interfacing it with both the circuit (eight-bit FIFO) and the computer (Tcl opening a MS-Windows COM1:-type device). I highly recommend it.See also Serial Port for an opportunity to access USB via a virtual com port (VCP) driver. -- RJMslebetman Using the VCP driver for the FT245 on Windows I managed to push around 840kb/s from Tcl. The limiting factor appears to be the recieving end which is a small microcontroller with a 5MHz instruction cycle. Tcl's I/O is very fast!APN On Windows, TWAPI's start_device_monitor command can be used for notifications when USB devices are inserted or removed.