I need to read UART data from one device, and send different data to the other device, all via raspberry pi zero. It has only one UART TX and one UART RX on GPIO pins, but I heard that it is possible to accomplish such thing. I need to use only GPIO pins (Micro USB + FTDI is not an option). Can someone suggest an option? I need to fully communicate with one device (RX+TX), and only listen to the second device (RX only).
I suggest you use the hardware UART (pins 8/10, GPIO 14/15) to communicate with the read/write device.
As long as the receive baud rate is 19.2kbps or less you should be able to use pigpio to read data from the read only device. Higher rates may also work but you are likely to have the occasional error.
You can use any spare GPIO for the read device.