What is the ruling on designing or downloading a program onto another person's computer that can be used for permissible things, for what pleases Allah, or for what displeases Allah?

The basic principle is that it is permissible to design and download computer programs, unless it is highly probable that they will be used for something forbidden. In that case, it becomes forbidden, in accordance with the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."