“Too much time is spent manipulating data just to get analysis and visualization tools to read it. Wrangler is designed to accelerate this process: spend less time fighting with your data and more time learning from it. Wrangler allows interactive transformation of messy, real-world data into the data tables analysis tools expect. Export data for use in Excel, R, Tableau, Protovis, …”
Seeing how this is from Stanford University, there’s a nice paper as well, “Wrangler: Interactive Visual Specification of Data Transformation Scripts”. There’s a bit of an overlap between FreeBase’s Gridworks (now Google’s Refine tool) but really, more differences than similarity. But they both work in your browser–try Wrangler right now.