OPC Server

OPC Server screenshots

OPC Server offers a wide variety of servers available for free
General view
OPC Server 1.0 : General view

Alternative downloads

Automated Solutions Modbus/TCP Master OPC Server
OPC Server provides Ethernet connectivity to Modbus/TCP Servers (Slaves).
Softing S7-S5 OPC Server
You can operate, visualize and diagnose your controllers.
Seneca OPC Server IO
Configuration and maintenance software.