Berkshelf
A cookbook source structure manager for Chef, similar to Bundler for Ruby. Each Chef cookbook can be structured as an individual entity and can be pulled into your main Chef workflows.
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Buildstep
Buildstep uses Docker and small buildpack scripts to build applications like Heroku. It was used by Dokku to create a 100-line Heroku clone. There are many open source Buildpack scripts for various languages like Java, Ruby, Erlang, PHP, etc.
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FastForward
Flexible operating-system event and metric forwarding agent. Receives input and forwards output using plugins.
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Fog
The Ruby Cloud API library. Provides a Ruby API for interacting and managing many cloud providers, such as spinning up new instances, terminating old ones, attaching storage, etc. Currently supports more than 20 providers, including EC2, Rackspace, Brightbox, etc.
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Foreman
A complete lifecycle management tool for servers, both self-hosted and in the cloud. It allows you to create and manage instances, build and deploy images, view and audit hosts, and much more! It works with Puppet or Chef, and has multiple interaction facilities like a web frontend, CLI and a RESTful API.
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GitLab
GitLab is an open-source, fully featured git web frontend developed using Ruby on Rails. You can host this in your own server, create projects, repositories and teams, manage fine grained access permissions, add wikis, collaborate, raise and merge pull requests, and do much more through the web! (Note: GitLab acquired Gitorious, another open source git management system, in March 2015)
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Instrumental
Instrumental is a real-time, high-scale application and server monitoring tool with intelligent alerts, a powerful query language, and free development accounts.
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Librarian-Puppet
Librarian-Puppet is a source structure and dependency manager for Puppet modules, similar to bundler for Ruby. Each Puppet module can be managed as a separate source repository with individual versioning, and can then be pulled into your Puppetfile.
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Opskeleton
Bootstrap a DevOps infrastructure with some opinionated defaults (vagrant, puppet, librarian-puppet, git, etc), standard development guidelines, etc. Makes it very quick to get a DevOps team up and running
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Pallet
A tool to provision and maintain servers across various cloud platforms as well as virtual machine platforms, without any dependencies. Provides cloud and operating system independence.
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Phabricator
Phabricator is an open source collection of development and code management, including code reviews and audits, browsing repositories, tracking bugs, etc
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