Gridcoin Research v3.5.7.9 - Mandatory Testnet Upgrade
With new security features enabled (e.g. - private key generation), and faster load times, you'll want to upgrade to the latest $GRC wallet right away.
Released on September 27, 2016:
Windows: http://download.gridcoin.us/download/downloadstake/GridcoinResearch.msi
Mac: see last page in thread: https://cryptocointalk.com/topic/13139-os-x-builds-feedback-bug-reporting/
Source: https://github.com/gridcoin/Gridcoin-Research
Linux: http://wiki.gridcoin.us/Linux_guide
Website: http://gridcoin.us/#Downloads
CryptoCoinTalk announcement: https://cryptocointalk.com/topic/40141-testnet-research-age/page-34
Don't forget to add the official node for testnet : "addnode=testnet.grcnode.co.uk", and the command "testnet=1" to your .conf file to initiate testnet.
Be advised that another blockchain will load into your chosen directory, so make sure you have space!