Acorn Universal Networking (AUN) is a network technology to allow Acorn specific protocols to be moved over the widely used protocol; TCP/IP.
As the modules which implemented these protocols evolved they were released as disc based updates to the copies in ROM, and often needed corresponding updates to the Messages text in ResourceFS. The AUNMsgs module provided a single module which registered several Messages files on behalf of those modules.
The majority of modules now manage their own updates in ResourceFS, meaning AUNMsgs is largely redundant.