OPC Unified Architecture (OPC UA) is an open, implemented under GPL 2.0 license, machine to machine communication protocol for industrial automation developed by the OPC Foundation.
The OPC UA protocol specification consists of 14 documents for a total of 1250 pages. Due to this complexity, existing implementations are usually incomplete.
This is why we were puzzled to see on Twitter post by Selftronics that they made OPC UA server running on ESP32-EVB!
Here are the details of the implementation, the sources are at GitHub.
olimex 
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