OpenOpcUa literally Open Source for OpcUa. First remember that Open is different than Free. OpenOpcUa is an initiative launched in 2009 by a consortium of international companies led by Michel Condemine (4CE Industry). The objectives of this consortium are multiple:

• Create a professionnal quality codebase implementing OpcUa concept
• Help users understand OpcUa technology
• OpenOpcUaCoreServer was the first
  Certified Open Source OPC UA Server.