Microsoft Dynamics GP 2013 Product Download Page - https://mbs.microsoft.com/customersource/northamerica/GP/downloads/service-packs/MDGP2013_Release_Download
The Inside GP blog has been covering the new features for quite a while now, and I highly recommend checking it out - Inside Microsoft Dynamics GP .
Siva has more details and lots of resources - Dynamics GP 2013 R2–Released Today!!
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