Serial Port Monitor is divided into Standard, Professional and Company Editions.

The difference you can see here:

Number of computers per license1110
Any serial port software/hardware can be analyzedyesyesyes
Monitor any number of serial ports at onceyesyesyes
Supports all COM-port typesyesyesyes
Intercepts all data read from/written to COM portyesyesyes
Monitoring serial ports which are already in useyesyesyes
Sending/receiving data to/from any COM port (Advanced Send Dialog)yesyes
The possibility to change COM port parameters from Advanced Send Dialogyesyes
1 license can be installed on 10 computersyes