Steam is not only a social-providing software that allows you to talk with people through text, voice chats (although stuffty quality) and even multiple persons chats, it also allows you to buy and store games onto your own account (which you should hold on to with your life).
Xfire on the other hand does not have any store of any sorts. It isn't a DRM program that lets you buy games that are stored onto a virtual account forever. But it DOES have uncompressed voice quality for voice chats (unlike Steam) and allows for recording of screenshots or videos in-game (except you need a good computer).
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