Comment by ruslan
Get two FTDI FT232RL chips, connect them together on serial side (RXD->TXD, TXD->RXD, GND<->GND). Plug into USB ports of your computers, run terminals (or any other software that supports serial I/O), send/receive data. Can use XYZModem to send files, PPP for TCP/IP networking, etc. No programming involved. Cheap as hell.
Thanks for the idea. I think it's a great one, but I have a few concerns:
1) The two computers are on 2 different grounds, so I believe it could damage the computers. So I would like to isolate the ground somehow, I am not sure what the options are. I tried to look for opto-isolated options, but didn't really find something clear. Do you have any suggestion?
2) This specific chip is marked NRND (not recommended for new designs) on ftdi's website, So it feels slightly wrong to use it?