RabbitMQ is open source message broker software (i.e., message-oriented middleware) that implements the Advanced Message Queuing Protocol (AMQP) standard. The RabbitMQ server is written in Erlang and is built on the Open Telecom Platform framework for clustering and failover.

HipChat is a hosted private chat service for your company or team. Invite colleagues to share ideas and files in persistent group chat rooms. Get your team off AIM, Google Talk, and Skype — HipChat was built for business. Note that HipChat auto-updates itself after an initial install.

Pidgin is a chat program which lets you log in to accounts on multiple chat networks simultaneously. Pidgin is a GTK+ instant messaging application for Windows and Unix. It supports AIM, ICQ, Jabber/XMPP, MSN, Yahoo!, Bonjour, Gadu-Gadu, IRC, QQ, SILC, SIMPLE and more. See http://pidgin.im/about for more information.

From Wikipedia on 2013-04-18: Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application for Windows, Linux and Mac OS X. It supports several popular instant messaging and telephony protocols, including open recognised encryption protocols for chat (OTR) and voice/vide... More information

Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecoms, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution and fault tolerance. OTP is set of Erlang librari... More information

Miranda IM is a multi-protocol instant messaging client for Windows. Very light on system resources and extremely fast, Miranda IM requires no installation and can be made to fit on a single floppy disk or USB drive. Featuring a powerful plugin-based framework and boasting over 350 plugins, Miranda IM is one of the most flexible and customisable me... More information

Boxstarter's Bootstrapper module provides a powershell wrapper that supports reboots and automatic logons and exposes commands that can detect pending reboots, perform logging and messaging, and several commands that can configure various windows settings.

Windows Essentials is a suite of free software by Microsoft, that helps you do more with photos, movies, instant messaging, email, blogging, and family safety. It includes Windows Movie Maker, Photo Gallery, Messenger, Live Mesh, and more.