While looking into the gp32 just now, I found mention of a small, internet-ready O/S aimed at "very constrained systems". Contiki is a complete operating system running happily in 64k systems, and was originally developed for the C64. It features multi-tasking, tcp/ip, telnet, and web-browser (among other things).
I was just a little surprised that there's no ZX port listed, especially considering there are versions for other 8-bit machines (vic20, atari, etc). So, anyone up for a new project??