Pedantry noted. It's probably better describing the SheevaPlug as the device that fostered the trend towards plug computing rather than the one that encouraged device hacking as my statement would imply. I mistakenly omitted the key detail that the Dockstar was a custom piece of hardware that was based on the SheevaPlug... Same SOC and features.
Those were the days! I was the first to hack in to get root on that little box but others took it much further than me!
http://batbox.org/nslu2-linux.html
I still have a couple around, but rarely turn them on.
Not to be pedantic, but before the Sheevaplug, there was the Linksys NSLU2, which came out in 2004:
https://en.wikipedia.org/wiki/NSLU2
http://www.nslu2-linux.org/wiki/FAQ/FirmwareMatrix