I'm a big fan of computercraft. You can quickly build turtles (robots) and program them to do almost anything a player can do. So you can automate almost everything and it's really fun. (Also in Lua.)

Open computers does have robots, but they are much more difficult to actually build, and have more constraints. I did try to get into OpenComputers, but everything felt so much more limited and expensive, and I just wanted to program cool things.

Was more impressed that it's part of the system architecture from the start, instead of being grafted into the setup later.