Limestone in the traditional sense is a type of sedimentary rock, consisting of layers and layers of “schtuff” mushed together. This is perhaps why the word was chosen for Microsoft’s Office internal scaffolding. The software, which actually leaked under the radar back in Office 14 beta days, appears to have been developed for the purpose of testing each and every layer of the Office suite – ranging from the basics like text formatting to the more complex Ribbon and Backstage UIs. Judging by the screenshots, it’ll never be a consumer facing application or magically integrate anything with everything. It’s simply a fun dev. tool.
(This particular build of Office 14 (14.0.4302.1000) doesn’t uninstall properly, therefore I used an older Windows Vista virtual machine I had lying around for screenshot purposes.)