Serial Splitter 

Use Serial Splitter to split serial ports at one side into multiple virtual and real serial ports at the other one, as well as join multiple serial ports into one. The unique feature of this version is many-to-many ports splitting/redirection.
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VSPD.net 

Network Virtual Serial Ports Driver is an advanced utility, the purpose of which is to emulate null-modem cable on computers located in a TCP/IP LAN or connected to the Internet by creating any number of pure virtual serial ports in your system.
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