ELTIMA Shared Serial Port

From Eltima Software:

ELTIMA Shared Serial Port: Shared Serial Ports is an advanced utility, the purpose of which is to share real serial ports between multiple applications in the way, that all applications will receive same data from real serial port simultaneously. It is achieved by creating virtual serial ports, which are same copies as real one. Each application will think that it is working with serial port in exclusive mode. All virtual serial ports will be able also to send data to real serial port. Also, you will be able to set permissions to read, write or change control lines state for every application separately.