grump is a very simple program for interacting over a serial port.
I use it at work to communicate with boards that I am developing on.
Basically, all it does is pass characters up and down the serial port. It has one obvious restriction, which is that if you type CTRL-C at it, it both sends CTRL-C and also exits. In most cases, CTRL-/ can be used to the same effect, without exiting grump.
Since I use the program to my own purposes, its defaults are set up to my convenience. In particular, the default speed and serial device are those values that tend to work locally (working with beagleboards and a USB serial connection on a PC running Ubuntu).
Use grump -h to find out details of its usage.
So far as I am concerned, this program is available as public domain code - use it as you wish, but it has no guarantees of being fit for use by anyone else.