The spreadsheets are open software in the sense that all their contents are exposed to the user.  Since they can be unlocked without a password, this allows users to customize the spreadsheets to their preferences.  We have heard from customers who are in fact doing so by combining several spreadsheets into single multitab documents.  This automatizes the transfers of data between separate calculations and bypasses the need of manually copying data between spreadsheets.  For portability (and other) reasons, I decided early in the project's development not to bundle separate calculations into multisheet workbooks in this manner, since not all Excel-like apps support this feature.  However, if your app indeed can handle multisheet documents, feel free to create new such spreadsheets to better suit your needs.  We'd always like to hear from you about your experiences with the suite.  And who knows, if you share your insights on this blog, that may get you in contact with other fellow Excel celestial navigators, so you can exchange ideas, and make even more progress!