ejabberd SaaS - Realtime XMPP and MQTT Software and Infrastructure as a Service.
Apache Vysper - Apache Vysper aims to be a modular, full featured XMPP (Jabber) server.
Prosody - Prosody is a modern flexible communications server for Jabber/XMPP written in Lua.
Openfire - Openfire (formerly Wildfire) is a cross-platform instant messaging (IM) and groupchat server.
Matrix.org - Matrix is an open standard for decentralized persistent communication over IP.
SAP NetWeaver - SAP NetWeaver enables the composition, provisioning, and management of applications across a heterogeneous software environment