ConDep
ConDep is a open source infrastructure configuration and deployment DSL (Domain Specific Language) specifically targeted to (but not limited to) the Windows Server platform. If your familiar with tools like Chef and Puppet, ConDep does very much the same, but with native support for Windows.
windows open-source ci provisioning config-mgmt net
ConfigCat
ConfigCat is a feature flags as a service. It gives you a web based dashboard to manage your feature flags + SDKs to integrate those feature flags into your applications. ConfigCat enables you to use the same feature flags in your mobile apps, websites and server-side applications. It offers all features for free. You get an enterprise-ready SLA with the pricing plans.
linux osx windows open-source free commercial ci cd config-management go java net nodejs php python ruby
Hubot
Hubot is a chat bot that can be configured to do a variety of tasks. Apart from usual CI stuff like deploying, it can be interestingly configured to do different workflows like posting images, translating languages and integrating with Google Maps, and being a bot, it can be configured to ask questions like what is the current deployed version, etc.
linux windows osx open-source ci nodejs
Phabricator
Phabricator is an open source collection of development and code management, including code reviews and audits, browsing repositories, tracking bugs, etc
linux osx open-source scm php
Rex
A agent-less server orchestration tool built on Perl
linux windows osx open-source orchestration perl