Messages Server

Messages Server is a component of OS X Server from Apple Inc. It was first introduced as iChat Server with the release of Mac OS X Server 10.4, and was upgraded to version 2 with the release of Mac OS X 10.5 Server in October 2007.
iChat Server was originally based on jabberd 1.4.3 and is named after Apple's iChat online chat client software.
Version 2 of the software is based on jabberd2 2.0s9 and supports server federation, which allows chat clients to talk directly with other systems that support XMPP. It also supports server-based chat archiving.
Server 5.7.1, the version aligned with macOS 10.14 and released on September 30, 2018, removed the Messages Server functionality from Server.app.