Indico
Indico is a general-purpose event management web-based solution. It includes a full-blown conference organization workflow as well as tools for meeting management and room booking. It provides as well integration with video-conferencing solutions.
A list of features can be found here. There is also a video!
Indico is free software, licensed under terms of the GNU General Public License (GPL) v3. It is currently in production at CERN, as well as in many other scientific institutions around the world.
Getting Indico
Information on how to get the latest release can be found at the project web site. If you are interested in contributing to Indico, you can consult the project documentation.
Community
The project web site is http://indico.github.io and the developers can be reached via IRC (#indico on Freenode).
History
Indico was created at CERN, originally as part of the European Union's InDiCo Project.