Muuri creates responsive, sortable, filterable and draggable layouts. Comparing to what’s out there Muuri is a combination of Packery, Masonry, Isotope and Sortable.
You can build pretty amazing layouts without a single line of JavaScript these days. However, sometimes (rarely though) CSS just isn’t enough, and that’s where Muuri comes along. At it’s very core Muuri is a layout engine which is limited only by your imagination. You can seriously build any kind of layout, asynchronously in web workers if you wish.
Custom layouts aside, you might need to sprinkle some animations and/or interactivity (filtering / sorting / drag & drop) on your layout (be it CSS or JS based). Stuff gets complex pretty fast and most of us probably reach for existing libraries to handle the complexity at that point. This is why most of these extra features are built into Muuri’s core, so you don’t have to go hunting for additional libraries or re-inventing the wheel for the nth time.
The long-term goal of Muuri is to provide a simple (and as low-level as possible) API for building amazing layouts with unmatched performance and most of the complexity abstracted away.