Yes, of course, it is completely open and you can use it for your necessities. It is not necessary to register to make submissions, but you should register if you want to have history of your previous submissions.

Yes, it is the same judge we use in the "theory of computation" subject at the university.

The original editor is from "Evan Walance": "http://madebyevan.com/fsm/". My colleague Carles Creus addapted it for our judge. Also, the original hightlighting engine comes from "codemirror", and it was also addapted by Carles Creus to our judge.

Thanks. Since the internet is full of texts and videos about these subject, we prefered not to make specific ones for this site. But we could do that. With respect to the editorial for problems, I suppose you mean an explanation on how to solve some concrete problems (the idea and the solution). I could try to prepare some videos about that.