jclouds is an open source library that helps you get started in the cloud and utilizes your Java or Clojure development skills. The jclouds API gives you the freedom to use portable abstractions or cloud-specific features.
jclouds tests support of 30 cloud providers and cloud software stacks including Amazon, GoGrid, Ninefold, vCloud, OpenStack, and Azure. Please see the complete list of jclouds supported providers that are supported by the jclouds API.

REPOSE is an open-source RESTful HTTP proxy service that scales to the cloud. REPOSE provides the solution to common API processing tasks such as rate limiting, client authentication, versioning, and logging so that web service developers can focus on the unique features of their services.

This is a comparison of Voice over IP (VoIP) software used to conduct telephone-like voice conversations across Internet Protocol (IP) based networks.

RetroShare is a Open Source cross-platform, Friend-2-Friend and secure decentralised communication platform.
It lets you to securely chat and share files with your friends and family, using a web-of-trust to authenticate peers and OpenSSL to encrypt all communication.
RetroShare provides filesharing, chat, messages, forums and channels

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.

Slurm is a highly configurable open-source workload manager. In its simplest configuration, it can be installed and configured in a few minutes