“Google treats its infrastructure like a state secret, so Holzle rarely speaks about it in public. Today is one of those rare days: at the Open Networking Summit in Santa Clara, California, Holzle is announcing that Google essentially has remade a major part of its massive internal network, providing the company a bonanza in savings and efficiency. Google has done this by brashly adopting a new and radical open-source technology called OpenFlow.”
So OpenFlow isn’t really “open source” software, it’s more of an open standard/API to program the forwarding tables of network devices. If a Layer 2/3 switch is OpenFlow capable, an OpenFlow controller can program the L2/L3/L4 rules through this API without involving routing protocols or such.
I don’t think there’s an open source OpenFlow controller, but there are closed sources ones, including one by NEC (seriously).