I'm the main contributor. There are others you can see in the GitHub graph but they are small.
There are many other users of the library but due to the project being OSS I have no comprehensive list. I can tell you from the Maven statistics that the client and server SDK have each been downloaded ~3000 times in the last month, by ~500-600 unique IPs.
The client has been production-ready since 0.2 release series. The server is now in production-ready as of 0.3 release series, but the API is not yet stable.
Development of the library is driven by necessity. I work for Inductive Automation (SCADA/HMI company) and we're using both the client and server SDK now.
Version 0.4 is under development, the main features being:
- generated new structures with hashCode, equals, builders
- the implementation of all the optional server diagnostics and their representation in the address space
- deprecation of AttributeDelegate and introduction of its replacement AttributeFilter / AttributeFilterChain
All of these features affect only the server SDK.