Earlier quoted context omitted.
GPIO pins. If you want to connect a "regular PC" to the real world, you can get a USB DAQ but even the cheapo LabJack, NI or MCC models are at least a hundred bucks.
A little microcontroller with USB support (I like the Raspberry Pi Pico) can help with your GPIO woes.
I have one of adadruit's RP2040 boards and use the REPL a lot to talk to other things connected to the i2c bus. For example, controlling servos from a servo board, or getting orientation data from an IMU. Basically, i treat the circuit python REPL like a command line