The OPC Test Client from Prosys will help troubleshoot OPC connections.
You can develop OPC compliant DA, AE and HDA Clients with C#/VB.NET.
This is a free stand-alone application which can be used for OPC Server testing.
The MatrikonOPC enables users to access OPC DA servers.
BACnet Objects can be read from any BACnet complient device on the network.
It is a toolkit that supports the most common interfaces and protocols of OPC.
"uForte OPC Client Toolkit" is a tool for rapid development of OPC DA clients.
It can store alarm data in a database for analysis.
The development Express Interface client applications is greatly simplified.