So, let’s say that you want to talk to an embedded device over the rs232 serial port, and you want a program like Hyperterminal or Putty for Linux. You’re in luck if you have “screen”! I’m going to assume you want to talk on COM1 at 115200 baud, with no parity, 1 stop bit, 8 data bits, and no flow control:
screen /dev/ttys0 115200 cs8 ixoff
The “no parity, 1 stop bit” part is the screen program’s default, and this is not settable (as far as I know). To enter a command (like “quit”), type “Ctrl+A” followed by a colon. See the screen man page for more details.