How to send Data to Arduino Nano?

I am trying to make a small external System Stats display with an Arduino Nano and a 16x2 LCD display. I will be running this in the background (Mac), so I won't have the Arduino IDE Serial Monitor open. What tools would I need to use for this?

Use any program on the Mac to send serial data to the Nano. Doesn't have to be the IDE.
Paul

I know, But what are those programs, or is there a way I could run a small python script in the background?