The Contiki Operating System and Desktop Environment by Adam Dunkels is an incredibly small (64k or less), lightweight (6510, Z80) computing environment for small, usually ancient systems. It currently runs at different levels of functionality on several different 8-bit systems, but the principal system on which it runs is the Commodore 64.
A list of the most notable features is as follows:
All of these will run on one Commodore 64
, without the support of any other computer.
The technical underpinnings to the system include a Multitasking kernel and TCP/IP support. This is all very amazing, of course, because this systems runs graphically on 64k of ram and a 6510 (6502 compatible) processor. (Amazing is relative; the first Unix ran in 11k, if I recall correctly.)
Of course, the Commodore 64 doesn't have a built-in network interface, so there is a board layout available for making an ethernet adapter from a $10 chip.
As for performance, it was noted somewhere (I remember not where) that the Contiki web site was hit by Slashdot, but that the Commodore 64 serving web pages at the time stayed up and kicking. (Stupot tells me that the server deals with a high load by silently dropping packets. So, high performance is not demonstrated as much as high pragmatism.)
Other and partial ports include:
I haven't had the opportunity to use it myself, but stupot informs me that he has, including an ethernet card.