Minecraft, Discord bots, etc. have already been mentioned; I will put in a plug for Cheat Engine and piracy. Much more dangerous and less ethical toys, but still highly educational. I learned almost 100% of my pre-college networking knowledge from BitTorrent. Cheat Engine has a very high learning curve but I'm sure it has acted as a gateway to other kinds of exploitation for other people. Although, I think with the rise of kernel Anti-Cheat this is a dying practice.