Multicom OEM
Multicom OEM is a programming interface, which allows you to add support of virtual serial ports to your own application. You have full control over ports created with the help of Multicom OEM, including reading data that some other application has written using WriteFile function, writing data... Now you can monitor all data that application writes to the port and redirect it to the real COM port. ... And vice versa, you monitor all data coming from device and redirect it to the virtual port. ... Just create one virtual port and tell the application to use it.
http://www.intellidriver.com/downloads/products/multicomoem.zip - 448Kb - Download

Virtual Null Modem
Null-modem cable is basically used for communication of two RS-232 DTE devices with each other. To create null-modem connection between the devices you need to use two computers or two serial ports of a single computer connected with null-modem cable. ... The most reliable way to create null-modem connection is using of virtual serial ports emulated by virtual serial port driver and null-modem cable. ... It is possible to create the unlimited couples of virtual serial ports on a single PC and connect them in any sequence using virtual null-modem cable.
http://www.virtual-null-modem.com/download/vnullmod20.exe - 1Mb - Download - Screenshot

DEKSI Modem Pooling
DEKSI Modem Pooling (DMP) is an advanced, powerful, and feature rich client-server software system that allows you to use any serial (COM) port on a remote computer from your local computer via a TCP/IP network connection. Sharing COM ports means sharing resources like modems, ISDN adapters, X. ... All data sent to these virtual ports is transferred to the DMP Server via a TCP/IP network connection and all replies from the real serial port on the server side are returned back to the DMP Client, so other applications will receive it as if it was sent from a real serial port.
http://www.deksoftware.com/new/dmp.zip - 2Mb - Download - Screenshot

Serial Port Terminal
Advanced Serial Port Terminal is a session-based, multi-purpose application that provides simple communication interface to connect to any serial port device (modem;fax;GPS;mouse;printer and so on). Whether you want to connect to remote computer using null-modem cable, send or receive various... Advanced Serial Port Terminal allows you to open as many serial ports as you like (including virtual serial ports); dynamically change serial port settings without necessity to close and reopen current port; adjust baudrate, databits, parity, stop bits, flow control parameters; save all received...
http://www.virtualserialport.com/download/serial_port_terminal.exe - 2Mb - Download - Screenshot

AlarIT Virtual Serial Driver .IP (AVSD.IP)
While the operation of different facilities, which are connected to a computer via serial port, there may appear the necessity to start up utility program (for these facilities) not in the machine, to which the facilities connect directly, but in the remote machine, that is connected to the... IP address of the receiving server, port number and the number of the real serial port on the receiver are specified on the client for each port. ... IP server is a service which realizes the exchange between a real driver of the serial port and TCP/IP.
http://www.alarit.com/downloads/products/avsdnet.zip - 576Kb - Download - Screenshot

Serial Port Monitoring Control
Serial Port Monitoring Control (SPMC) - RS232 Data Acquisition and Com Port Control Component Library, Modem Access Component. Connection Sniffer and Port Test Software Library. The library lets you enumerate all installed serial devices, including, but not limited to serial ports and modems. ... All kind of PnP serial devices as well as virtual devices are also supported. ... After you get an instance of the serial device, you can create a monitor object and attach to the device to receive monitored data and events.
http://www.hhdsoftware.com/Download/hhdspmc.exe - 470Kb - Download - Screenshot

ITS Net Serial Driver (ITSNSD)
While the operation of different facilities, which are connected to a computer via serial port, there may appear the necessity to start up utility program (for these facilities) not in the machine, to which the facilities connect directly, but in the remote machine, that is connected to the... IP address of the receiving server, port number and the number of the real serial port on the receiver are specified on the client for each port. ... Besides the data flow, TCP/IP transfers the overhead information about the condition of different signals on serial port physical contacts.
http://www.itsuperiority.com/downloads/products/avsdnet.zip - 576Kb - Download - Screenshot

HiFlyTechNet Serial Driver (HNSD)
While the operation of different facilities, which are connected to a computer via serial port, there may appear the necessity to start up utility program (for these facilities) not in the machine, to which the facilities connect directly, but in the remote machine, that is connected to the... IP address of the receiving server, port number and the number of the real serial port on the receiver are specified on the client for each port. ... Besides the data flow, TCP/IP transfers the overhead information about the condition of different signals on serial port physical contacts.
http://www.hiflytech.com/downloads/products/avsdnet.zip - 576Kb - Download - Screenshot

Alarit Net Serial Driver (ANSD)
While the operation of different facilities, which are connected to a computer via serial port, there may appear the necessity to start up utility program (for these facilities) not in the machine, to which the facilities connect directly, but in the remote machine, that is connected to the... IP address of the receiving server, port number and the number of the real serial port on the receiver are specified on the client for each port. ... Besides the data flow, TCP/IP transfers the overhead information about the condition of different signals on serial port physical contacts.
http://www.alarit.com/downloads/products/ansd.zip - 283Kb - Download - Screenshot

EXP Net Serial Driver (ENSD)
While the operation of different facilities, which are connected to a computer via serial port, there may appear the necessity to start up utility program (for these facilities) not in the machine, to which the facilities connect directly, but in the remote machine, that is connected to the... IP address of the receiving server, port number and the number of the real serial port on the receiver are specified on the client for each port. ... Besides the data flow, TCP/IP transfers the overhead information about the condition of different signals on serial port physical contacts.
http://www.explorinform.com/downloads/products/avsdnet.zip - 576Kb - Download - Screenshot