Based on the rules, this are the requirements the game must have:

-Done with Javascript

-Run in browser

-Code easy to understand

But I have questions about the software and the terms of use:

-Can it be done in ANY software that supports javascript and that include the code? 

I´m considering using RPG maker since it uses javascript but doesn´t have traditional scripts. 

As for the open source part, RPG maker may cost money but anyone can make plugins and customize it in any way. Does that count as "Open source" or should I use something like Unity instead?

Thanks

Yes you can. Sorry for the delay in the reply. You can use anything that runs in the browser as long as you post your source.