Apache Vysper is described as 'aims to be a modular, full featured XMPP (Jabber) server. It has highly modular design. The core of XMPP is defined in the standards RFC3920 and RFC3921. XMPP is more commonly known as 'Jabber'' and is an app in the Social & Communications category. There are seven alternatives to Apache Vysper for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and BSD. The best alternative is MongooseIM platform, which is both free and Open Source. Other great apps like Apache Vysper are Prosody (Free, Open Source), Openfire (Free, Open Source), ejabberd (Free, Open Source) and Tigase (Free, Open Source).
MongooseIM is aimed at large, complex enterprise level projects, where real-time communication is critical for business success. It provides high availability, ease of deployment, development and reliability in production.
ejabberd is an open source Jabber/XMPP server designed from the ground up to be the building bricks of highly critical messaging systems. Designed to be massively scalable, it is used to power web scale deployments across many software industries.
Jabberd project has been rewritten from the ground up to be scalable, architecturally sound and to support the latest X.M.P.P Extension Protocols coming out of the X.S.F ( XMPP-Standards-Foundation : foundation for XMPP standards ).