Do you know what Akinator is? 
I want to create similar thing, but instead of it guessing who the person is, I want it to generate a web app that have all the constraints in the questions.
What would be good questions for this kind of product?
Yes, I am familiar with Akinator. For a web app that generates constraints based on questions, you can ask questions that gather information about:

- User goals/objectives
- Available resources/technology
- User constraints (time, budget, scope)
- User preferences (design, functionality)
- Industry-specific requirements
- Target audience
- Security/privacy considerations

By asking these types of questions, you can gather the necessary information to generate a web app with constraints that meet the user's needs.
A different question now: how to make a Croque Monsieur healthier and lower in calories?
To make a healthier and lower calorie Croque Monsieur, consider the following tips:

- Use whole grain bread instead of white bread.
- Reduce the amount of cheese used or opt for a lower-fat cheese.
- Use a lighter version of the béchamel sauce, made with skim milk.
- Add more vegetables to the sandwich, such as spinach or tomato.
- Bake or grill the sandwich instead of frying it.

Let me know if there is anything else I can help you with.