Hello Everyone,
Has anyone used healthcare.gov for applying health insurance? Can we apply discounted health insurance?

It depends on what status you are in and how much you make? Go to healthcare.gov and check the info. Everything you need is there.

It seems that an estimated annual income has to be compared with a threshold, which I understand. I believe I would make more than the threshold, therefore, I do not seem to be eligible for discounted health insurance. But what if I buy non-discounted insurance but end with an actual annual income at the end of 2017 less than the threshold?

Your discount will be based on the a scale I think. It is not a hard number that if you cross that line you will not get benefits. Also, if you end up making less than I think you can get some tax credits back. I would urge you to apply and see how much discount you can get. You don't have to accept it. Do it while there is time. New administration might get rid of the whole thing.