We just released InstaDesk, an Instagram Client for the Mac. It can be bought on the Mac OS X App Store.

InstaDesk lets you not only browse your or your friends Instagram pictures, but easily explore the social graph and find new people to follow. With InstaDesk you can browse beautiful pictures, newest uploads of your friends, or interesting people to follow. Furthermore, you can comment on pictures, like them, download them, or watch them in slideshows.
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