Cobalt was the first in a line of \"internet SERVER appliances\" in that it was easy to set up and run multiple accounts for email, web-hosting and more. They were eventually bought by SUN Microsystems. Cobalt helped foster a lot of \"mom and pop\" ISPs in the early days of the web.
As with anything like this, they initially ran their own custom OS, which is tough to find online these days, but my understanding is that there are a few variants of Linux that can be put on these now, making them more secure.
However, this one does have it\'s RAM and a 20GB HD, so it might still have the old OS still on it (who knows?), maybe you can hack root and get it running on the original OS. Whatever. Or just collect as part of internet history.