Phabricator is an open source LAMP (Linux, Apache, MySQL, PHP) application that helps software companies build better software.
There is also a paid hosted version available.
Read Phabricator-Discuss. Plan. Code. Review.
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Pros
Pro Free and open source
Phabricator is completely free and open source. It's source code is hosted on GitHub.
Pro Actively updated
Phabricator is quickly improving, with bug fixes and new features added often. There is an update to the changelog every couple of weeks.
Pro Bug tracker is included
Includes a bug tracker out of the box. Allows for managing bugs, creating issues, commenting on them and closing them.
Pro Built-in Q&A platform - Ponder
Instead of having to have separate Q&A tool, there's Ponder which takes out the hassle.
Pro Built-in Wiki and pages support
Pro Fully customizeable workboard
You can configure your workspace to deal with tasks, bugs, todo's, etc.
Pro Supports the three major version control systems
Support for Git, SVN and Mercurial is available.
Pro Super flexible bussiness rules (Herald)
Pro Able to review graphical asset changes as well as code.
Pro Fine grained access control
With using Spaces and Project and custom policies you can have any combination of access to any object inside of your own Phabricator instance.
Pro Designed by software engineers for software engineers
The engineering workflow is far superior to Github style branching and merging. Phabricator separates local representations of the repository from remote, which enables a variety of workflow optimisations, like stacked diffs on a single branch.
Pro Code ownership
Users can subscribe to files or even repositories and notifications will be sent when code you are subscribed to is changed.
Pro Command line access (via ARC)
Pro Able to track design mockups
You can track not only code bud also design mockups.
Pro Built-in voting
You can create voting in an instant and need not to rely on external tools.
Pro Built-in blogging platform
There's a great platform which you can use to post stuff, or use as an internal blog, dev blog, release anouncement place and many others.
Pro Built-in chatrooms
Pro Able to manage legal agreements for open source projects
Cons
Con For someone who likes formality, this is not for you
Has slang, sarcasm, and other informal things. If you need to stay formal you shouldn't use this. Personally I like it but others may have different opinion.
Con Difficult to configure
Compared to a solution like Bitbucket Server (granted Phabricator offers more options), it is difficult to configure. Settings are scattered everywhere and you must drill down through several screens to find some of them. Documentation is very complete but also not always in parity with the application itself.