74HC4051 Alternative - 4 Channel 1 circuit?
This multiplexer is bi-directional, essential for your question as it's unclear whether the 'processor' is reading or controlling the transistors.

Alternatives in that family are 4052, which is two 4:1 muxes with common select inputs, and 4053 which is 3 fully independent 2:1s.

If the processor is controlling up to 8 peripherals, then the more usual way to do it is with a single directional logic device like a shift register, 595 is popular. You use 2 or 3 processor pins to load it with data, which is then available on all 8 output pins at the same time. With appropriate control, any pin can be manipulated independently.