The Animation and Rigging Toolkit (ART) has shipped with Unreal Engine from the beginning. We are now making it available on the marketplace so we can more quickly roll out updates and have a centralized place to get the latest version.
The Animation and Rigging Toolkit is used by Epic for all internal projects, including Fortnite, Paragon, Robo Recall, and Unreal Tournament. Autodesk Maya is required to use the tools (we use Maya 2016 internally), as is a Windows operating system. These tools allows you to rig and animate your own characters, with a robust suite of tools to make the process as easy as possible. These tools are fully compatible with the Epic Mannequin (he was built on them after all!), and all Epic skeleton animations available on the marketplace.