This is a gateway device for connecting your basic network to a USB storage device like an external hard drive or memory stick. It accepts up to two of these USB devices. Amazon is selling it at over half-off of list.
The official Linksys product page is here:
http://www.linksys.com/products/product.asp?grid=35&scid=43&prid=640
Since it's running a version of Linux, people have started making various modifications to the firmware to set up things like music servers. Here's one site that is tracking what the developers are doing:
http://www.batbox.org/nslu2-linux.html
