XMPP MUC Search:

Website: search.jabber.network
Search Engine for XMPP MUC Conference(s)

XMPP Network Status:

Website: xmppnetwork.goodbytes.im
Visualization of XMPP Network

XMPP Standards Foundation (XSF):

Website: xmpp.org
The XMPP Standards Foundation (XSF) is an independent standards development organization focused on the open standards for real-time communication, such as XMPP.

XMPP Software:

Prosody:

Website: Prosody.im
Prosody is a modern XMPP communication server. It's lightweight, easy to use, and designed for privacy and security.

ejabberd:

Website: ejabberd.im
ejabberd is a robust, massively scalable, and extensible XMPP server written in Erlang.

Openfire:

Website: Ignite Realtime
Openfire is a real-time collaboration (RTC) server licensed under the Open Source Apache License. It uses the only widely adopted open protocol for instant messaging, XMPP (also called Jabber).

XMPP Clients:

Conversations (for Android):

Website: Conversations.im
Conversations is a Jabber/XMPP client for Android smartphones that has been optimized for mobile devices.

Gajim (for Linux, Windows, macOS):

Website: Gajim.org
Gajim is a full-featured and easy-to-use XMPP client for Linux, Windows, and macOS.

Psi (for MS Windows, macOS):

Website: Psi Psi is an XMPP instant messaging client with a simple and stable user interface. It provides basic features such as one-to-one and group chats, file transfers, and presence notifications. Psi is characterized by its minimalist design and is suitable for a wide range of users.

Psi+ (for GNU/Linux, MS Windows, macOS, FreeBSD and Haiku):

Website: Psi+ Psi+ (Psi Plus) is an evolution of the original Psi client aimed at providing additional features and enhancements. Compared to the base Psi client, Psi+ offers advanced features such as improved encryption options, enhanced chat management tools, and various UI customization options. Psi+ development is typically community-driven, with user needs and suggestions considered to introduce new features and improvements.

XMPP Libraries:

Smack (Java):

Website: Ignite Realtime - Smack
Smack is an open-source, highly modular, and easy-to-use XMPP client library written in Java for Java SE compatible systems.

SleekXMPP (Python):

Website: SleekXMPP
SleekXMPP is an elegant Python library for XMPP (aka Jabber, Google Talk, etc.).

XMPP Extensions (XEPs):

Website: xmpp.org/extensions
XEPs are XMPP Extension Protocols, specifications for functionality that can be added to an XMPP server or client.

XMPP Compliance Tester:

Website: Compliance Tester
This tool allows you to test XMPP server and client implementations for compliance with the XMPP standards.