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!

Pdsh is a high-performance, parallel remote shell utility. It uses a sliding window of threads to execute remote commands, conserving socket resources while allowing some connections to timeout if needed.

Nodediag provides an extensible TAP framework for executing node diagnostic checks at system startup.

ConMan is a serial console management program designed to support a large number of console devices and simultaneous users.

CRM114 is a system to examine incoming e-mail, system log streams, data files or other data streams, and to sort, filter, or alter the incoming files or data streams according to the user's wildest desires. Criteria for categorization of data can be via a host of methods, including regexes, approximate regexes, a Hidden Markov Model, Orthogonal Sparse Bigrams, WINNOW, Correllation, KNN/Hyperspace, or Bit Entropy ( or by other means- it's all programmable).

documentr is a free, open-source, Web-based tool to edit and present software documentation. It allows to easily maintain documentation for multiple products and product branches.

SemanticScuttle is a social bookmarking tool experimenting with features like structured tags and collaborative tag descriptions.

Kamailio is able to handle thousands of call setups per second. Among features: asynchronous TCP, UDP and SCTP, secure communication via TLS for VoIP (voice, video); IPv4 and IPv6; SIMPLE instant messaging and presence with embedded XCAP server and MSRP relay; ENUM; DID and least cost routing; load balancing; routing fail-over; accounting, authentication and authorization; support for many backend systems such as MySQL, Postgres, Oracle, Radius, LDAP, Redis, Cassandra; XMLRPC control interface, SNMP monitoring. It can be used to build large VoIP servicing platforms or to scale up SIP-to-PSTN gateways, PBX systems or media servers like Asterisk™, FreeSWITCH™ or SEMS.

This is the world's first open source HTML5 SIP client entirely written in javascript for integration in social networks (FaceBook, Twitter, Google+), online games, e-commerce websites...
The client can be used to connect to any SIP or IMS network from your preferred browser to make and receive audio/video calls and instant messages.

Ganeti is a cluster virtual server management software tool built on top of existing virtualization technologies such as Xen or KVM and other Open Source software.

Froxlor: The server administration software for your needs.
Developed by experienced server administrators this open source (GPL) panel simplifies the effort of managing your hosting platform.

The Floodlight controller is an enterprise-class, Apache-licensed, Java-based OpenFlow Controller. It is supported by a community of developers including a number of engineers from Big Switch Networks.

OpenFlow is a open standard managed by the Open Networking Foundation (ONF).  It specifies a protocol through switch a remote controller can modify the behavior of networking devices through a well-defined “forwarding instruction set”.  Floodlight is designed to work with the growing number of switches, routers, virtual witches, and access points that support the OpenFlow standard.