What do you mean preview? You could look at it with a text editor. You could strip the mark up and just look at the text. You could write an HTML viewer using something like Tk, but then you start crossing the line into browser territory. You could leverage IE or Firefox to render the HTML for you "under the hood" - is that using a browser? You could open the HTML directly with something like Firefox, but then you really are using a browser.

Yes, the question is silly. Is is silly because it doesn't provide enough context. A good answer needs the question to say why you want to do that and why you can't just use a browser.