Using rsync and hard links, it is possible to keep multiple, full backups instantly available. The disk space required is just a little more than the space of one full backup, plus incrementals.

Mistserver is a lightweight, open-source multistandard multimedia server. It bridges the gap between lightweight webservers and the usually heavyweight mediaservers that support non-HTTP protocols.

ownCloud gives you universal access to your files through a web interface or WebDAV. It also provides a platform to easily view & sync your contacts, calendars and bookmarks across all your devices and enables basic editing right on the web. Installation has minimal server requirements, doesn’t need special permissions and is quick.

OpenNMS is an award winning network management application platform with a long track record of providing solutions for enterprises and carriers.

FAI is a non-interactive system to install, customize and manage Linux systems and software configurations on computers as well as virtual machines and chroot environments, from small networks to large-scale infrastructures like clusters and cloud environments.

The Transparent Inter Process Communication protocol allows applications in a clustered computer environment to communicate quickly and reliably with other applications, regardless of their location within the cluster.

Castle is a key-value store responsible for redundancy, caching, indexing and disk layout management. Acunu uses it to store all user data as well as statistics captured and displayed by the Control Center.
Castle is not cluster aware and thus it doesn’t participate in distributing data in a cluster. However, Castle interfaces are designed with distributed databases in mind, featuring timestamps and automated discarding of old, deleted data.

OneSwarm is a P2P file sharing service that protects your privacy. It's fast, BitTorrent-compatible, and free!