Vagrant is a system to create reproducible and portable development environments. Because of the variety of systems used for Habitica development and the various issues developers may encounter setting up Habitica on them, vagrant provides a single development enviroment with minimal dependencies on the developer's local platform. It can be used on a variety of systems including Windows, Mac OS X, and Linux.
Instructions for using the Habitica Vagrant environment are in Setting up Habitica Locally.