rs232

Professional cross-platform serial port utility for communication, monitoring and debugging.

Vovsoft Serial Port Monitor is an easy to use utility that allows monitoring your computer's COM port data traffic. You can read serial data from any COM port and send data to any COM port.

netcat for serial ports — a command-line serial terminal.

Termite is an easy to use and easy to configure RS232 terminal. It uses an interface similar to that of "messenger" or "chat" programs, with a large window that contains all received data and an edit line for typing in strings to transmit.