Shareable Dynamic Media is our vision for an interactive computing environment that blurs the distinction between documents and applications, characterized by three key properties: malleability, so that users can appropriate and repurpose media in idiosyncratic ways; shareability, so that users can collaborate on any type of content; and distributability, so that users can access and manipulate media across diverse devices and platforms. Webstrates is a prototype web-based environment designed to explore this vision. It supports real-time sharing of any web content, as well as transclusion to flexibly combine and assemble multiple media together. The demonstration illustrates the power of Webstrates and Shared Dynamic Media through several scenarios, such as collaborative authoring, distributed slideshow presentation with audience participation, collaborative programming, and shareable window management.