Free: Communicate with RS232, RS422, RS485 and Modbus serial devices.

The comDebug program lets you communicate with almost any RS232, RS422,
RS485 or Modbus serial device. What's more, it's free! Its extensive
trouble-shooting capabilities make it ideal for solving comms problems, or
for quickly checking that you can communicate with your instrument before
starting to automatically acquire data.
# No programming required
# Free technical support for life
# Easy to use
# Understands ASCII or binary data
# For serial instruments that continually send data and those that need
prompting
# Quickly identify and correct communication errors
# Insert cyclic redundancy checks (CRCs)
# Send ASCII values, 16-bit 2s complement integers, unsigned integers,
single bits of data, etc, to instruments
# Control the state of the PC's serial port output lines
# See the state of the serial port input lines
# Send acknowledgements
# Save settings in a file
# Full hypertext Help
# For Windows 95 and later