OPC UA security: a practical model for certificates, users, and trust
A field guide to OPC UA application identity, encrypted channels, user authentication, trust lists, and the operational work that keeps them healthy.
Kepware
Multi-protocol connectivity server, now part of Velotic.
Industrial connectivity software exposing hundreds of device and PLC protocols through OPC UA, MQTT, and other northbound interfaces. Originally by PTC, now part of Velotic alongside Proficy and ThingWorx.
See also: OPC UA · Edge gateway · Velotic
Use the concept: Industrial data connectivity: from register to consumer · Industrial data contract template
In depth
OPC UA, MQTT, and Sparkplug B: how they fit together
Three technologies that get compared as rivals but usually work as layers. What each one owns, and how to stop choosing between them.
OPC UA companion specifications: a guided tour
The base standard models anything; companion specs model your industry. How to find, read, and actually use them.