As you all mentioned above the main difference between Patent and NDA, That Patent protects your ownership of the idea not only on a project base but all over that no one can duplicate or claim your idea. also, you can collect money from companies want to integrate the idea in their design. for example, my current company is the one who designed the idea of the nano USB connector. so most of you using it for wireless mouses. And they do collect money from all other companies using the idea like Logitech. On the other hand, NDA is more to protect a project based and a mutual agreement. for example, We need it when you work with the company on a probatory design or highly confidential information. But If we don’t sign it and work on the same idea, we have no legal issue against us.