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. ... The program emulates one or more couples of RS-232 serial ports connected via virtual null-modem cable.
http://www.virtual-null-modem.com/download/vnullmod20.exe - 1Mb - Download - Screenshot

Virtual Serial Port Kit
Virtual Serial Port Kit creates pairs of virtual serial ports in your system which are virtually connected to each other. Physical null modem cables are not required. You can connect any number of virtual port pairs. Virtual serial port pairs will look and work exactly like real hardware serial... Virtual Serial Port Kit is useful also for users which work with Windows applications using serial COM ports joined by null modem cable especially if those applications require more than one serial port pair.
http://www.virtual-serial-port.com/virtual-serial-port-kit.zip - 796Kb - Download - Screenshot

Virtual Serial Port Driver XP4.5
Virtual Serial Ports Driver XP creates two pure virtual serial ports in your system which are virtually connected to each other. For other Windows applications, virtual ports will be seen exactly as two real serial ports connected via null-modem cable. ... Virtual link between virtual serial ports is much faster then real null-modem cable connection and depends on your processor speed. ... With user-friendly GUI and on-the-fly help of Virtual Serial Port Driver XP it's very easy to configure a virtual serial ports pair.
http://www.mks.zp.ua/vspdxpd.exe - 1Mb - 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

Virtual Serial Ports Driver CE
Virtual Serial Ports Driver CE creates up to 20 pure virtual serial ports in your mobile system, this results in up to 10 virtual serial ports pairs. Each pair has 2 ports that are virtually connected to each other. For other applications, virtual serial ports will be seen exactly as two real... In this case all data sent by other applications to virtual serial port COM5 (VSP0) will arrive at virtual serial port COM6 (VSP9), and all data sent to virtual serial port COM6 will arrive at virtual serial port COM5 (VSP0).
http://www.eltima.com/download/vspdce.exe - 432Kb - Download - Screenshot

REMOTE DRiVE
REMOTE DRiVE is the Emergency-Access tool No. 1 for Windows NT/2000 and Windows XP. If Windows NT/2000 or Windows XP machine fails to boot and you need important data very fast you can use to copy them over a serial or a parallel link cable. Additional you can run User Manager, CIA Unerase or... The HOST and CLIENT machines must be connected with a standard parallel link cable or null-modem serial cable. ... Easy administrative access any computer (FAT, FAT32 and NTFS) over the parallel or the serial cable connection.
http://www.matcode.com/remdrive.exe - 474Kb - Download - Screenshot

Multicom
Multicom is appointed for emulation of one, two or more (up to 200) serial streams. Hardware devices are not necessary. This product is based on Windows XP DDK and doesn't require using devices of other manufacturers. The whole product is created with the help of Microsoft tooling. ... Multicom realizes full emulation of Serial Port functions, connected with each other with the help of NULL-MODEM or full cable, including DTR, CTS, DSR, RTS. ... Also, it will be interesting for developers of the products appointed for connection of two or more computers through serial ports.
http://www.intellidriver.com/downloads/products/multicom.zip - 448Kb - Download

AVSD
AVSD is appointed for emulation of one, two or more (up to 200) serial streams. Hardware devices are not necessary. This product is based on Windows XP DDK and doesn't require using devices of other manufacturers. The whole product is created with the help of Microsoft tooling. ... AVSD realizes full emulation of Serial Port functions, connected with each other with the help of NULL-MODEM or full cable, including DTR, CTS, DSR, RTS. ... Also, it will be interesting for developers of the products appointed for connection of two or more computers through serial ports.
http://www.miraclit.com/avsd.zip - 448Kb - Download

AlarIT Virtual Serial Driver (AVSD)
AlarIT Virtual Serial Driver is appointed for emulation of one, two or more (up to 200) serial streams. Hardware devices are not necessary. This product is based on Windows XP DDK and doesn't require using devices of other manufacturers. The whole product is created with the help of Microsoft... AlarIT Virtual Serial Driver realizes full emulation of Serial Port functions, connected with each other with the help of NULL-MODEM or full cable, including DTR, CTS, DSR, RTS. ... 0 with null-modem cable showed that they are practically identical.
http://www.alarit.com/downloads/products/avsd.zip - 448Kb - Download

Virtual Serial Port Driver XP4
Virtual Serial Port Driver XP4 creates two pure virtual serial ports in your system which are virtually connected to each other. For other Windows applications, virtual ports will be seen exactly as two real serial ports connected via null-modem cable. ... 0 you can connect one application to another using virtual serial ports pair. ... With Virtual Serial Port Driver XP 4. ... Of course, you can transfer files, other data or do whatever you want as it was real serial ports. ... Applications will be able to exchange data.
http://www.virtualserialport.com/download/vspdxp.exe - 1Mb - Download - Screenshot