The Prisoner Ransom Mod allows you to demand ransom, in silver, for prisoners at the comms console. Ransom won’t work if the faction is very hostile to you (the threshold is around 90%).
Returning a prisoner will give you a slight relationship boost with that faction. Leaders are worth more and will likely be more friendly to you after that. But if the faction doesn’t take your demands seriously they will raid you.
The Prisoner Ransom Mod was originally created by Erdelf.