Tigase is described as 'open source (AGPL3) project started by Artur Hefczyc in October 2004 to develop an XMPP server implementation in Java' and is an app in the Social & Communications category. There are eight alternatives to Tigase for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and Android. The best alternative is Matrix.org, which is both free and Open Source. Other great apps like Tigase are MongooseIM platform (Free, Open Source), Prosody (Free, Open Source), Openfire (Free, Open Source) and ejabberd (Free, Open Source).
Matrix defines a set of open APIs for decentralised communication, suitable for securely publishing, persisting and subscribing to data over a global open federation of servers with no single point of control.
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.
Apache Vysper 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'.
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 ).