Open-source scientific workflow and provenance management system that provides support for simulations data exploration and visualization. Whereas workflows have been traditionally used to automate repetitive tasks for applications that are exploratory in nature such as simulations data analysis and visualization very little is repeated---change is the norm. As an engineer or scientist generates and evaluates hypotheses about data under study a series of different albeit related workflows are created while a workflow is adjusted in an interactive process. VisTrails was designed to manage these rapidly-evolving workflows.A key distinguishing feature of VisTrails is a comprehensive provenance infrastructure that maintains detailed history information about the steps followed and data derived in the course of an exploratory task: VisTrails maintains provenance of data products of the workflows that derive these products and their executions. This information is persisted as XML files or in a relational database and it allows users to navigate workflow versions in an intuitive way to undo changes but not lose any results to visually compare different workflows and their results and to examine the actions that led to a result. It also enables a series operations and user interfaces that simplify workflow design and use including the ability to create and refine workflows by analogy and to query workflows by example.VisTrails supports the creation and execution of workflows. It allows the combination of loosely-coupled resources specialized libraries grid and Web services. The released version comes with support for several packages including VTK Image Magick Web Services and pylab. You can also download packages contributed by our users as well as create your own packages/modules. Workflows can be run interactively through the VisTrails GUI or in batch using a VisTrails server. VisTrails is written in Python and it uses the multi-platform Qt library for its user interface. It runs on Mac Linux and Windows.Provenance-rich results derived by VisTrails can be included in LaTeX Wiki Microsoft Word and PowerPoint documents.