Close source code

[Iron]

1. That was the original creator's request. She wanted her work to remain as she saw it, for people to experience it the way she intended it to be experienced.

2. Multiplayer. The more code access people have, the easier hacking becomes, and Uranium has a nice hack-free trading community, a breeding community, etc.

So yeah it will always be closed source.

Other games, like Reborn I think, have a different attitude where they encourage modding, and those games are cool in their own way. You can always find something you like in the fangame community.