http://en.wikipedia.org/wiki/COM_port_redirector
'Remote serial' is a way to use the serial port on another machine through the LAN. It uses the RFC2217 protocol. It needs a serial to network proxy running on the remote machine.
http://sourceforge.net/projects/ser2net/
Com0Com is an open source solution for Windows. The com2tcp redirector can be used as a serial port server on a remote Windows machine.
http://sourceforge.net/projects/com0com/
Ser2net can be used as a serial port server on a remote Linux machine and cyclades-serial-client can be used as a client connecting to this server. The serial client makes a symbolic link (/dev/modem) to a pseudo tty.
Ser2net can work with clients running on Windows machines. So far, I tested:
- Serial-Over-Ethernet Connector 3.2 (try before buy)
http://www.eltima.com/products/serial-over-ethernet/
- HW Virtual Serial Port (free)
http://www.hw-group.com/products/hw_vsp/index_en.html
- Cyclades-serial-client
The script file 'cyclades-serial-client' (version 0.92, 0.93) may have to be edited to make it work. Replace every occurrence of 'tsrsock' by 'cyclades-ser-cli'. Also, it seems that the socket number to use for the server should be the one used by cyclades-serial-client (see its config file).
While Cyclades-serial-client can be made to compile under NetBSD, I've not been able to use it.