GDC is a site for game designers to post their games, in what ever version state they are (alpha, beta, or gold/master), so the people may view and play them in order to give feedback on what they thought about the games and suggestions to game designers on what they can do to improve on them. Posting game designers may also post the concept art and screenshot for their games to get additional feedback on their in-production games and create blog posts to keep users of the site updated on the latest news of game production.
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GDC is also a site for non-game designers to view and beta-test games to give feed back for their creators; and also to see the different processes that game designers go through in order to create games that can be enjoyed and played by the public.