(Used) to / for

Hello everyone

Here is my question:

1. AJAX is a language for creating interactive web applications
2. AJAX is a language to create interactive web applications
3. AJAX is a language used for creating interactive web applications
4. AJAX is a language used to create interactive web applications

Could anyone tell me:

• Among the above sentences, which are correct and which are incorrect? (my guess: 1 & 4 are correct, 2 & 3 are not)
• Among the correct ones, which one are native speakers most likely to use?
• Is there a definite rule as to whether "to + infinitive" and "for + progressive infinitive" should be used?

Thanks for any help, I find myself constantly stuck on problems like this and it's annoying

I think as well that any of them is correct, but 1 sounds best imho.