Your home is filled with microprocessors that talk to each other over two-wire serial protocols. Your oven probably has a control panel that talks over I2C or some other serial protocol to a control module.
That credit card terminal on the shop counter has a modem that talks to another computer the old-fashioned way: frequency-keyed tones over a phone line.
Your car has more chips than you think, all talking over a shared serial bus like CAN or DBUS (not the desktop protocol, the Bosch one).
That touchscreen on your smart phone communicates with the host processor over a serial protocol.
In the embedded systems world it's cheaper and easier to use these ancient protocols than to try and install ethernet lines and TCP/IP stacks...just so that your oven can start a bake cycle.
