Espalier (formerly Object Spreadsheets) is a new computational paradigm that combines the usability advantages of spreadsheets with SQL-like expressive power, providing a way to build a wide class of interactive applications more easily than with existing tools.

Nearly every organization is responsible for processes that involve collection and manipulation of structured data subject to certain rules; in CSAIL and EECS alone, examples range from the graduate admissions process to a milk pool that tracks whose turn it is to buy milk next. The Espalier tool can be used to build "data-centric applications" that support these processes by letting users view and update data subject to the applicable constraints. Espalier seeks to provide an integrated visual environment to construct the schema, data, and logic that is natural enough to appeal to end-user developers yet general enough to conveniently express arbitrary logic. It is the first spreadsheet-based tool to support editing of hierarchical structured data (important in many applications) and a formula language with SQL-like expressive power.

There is a long history of tools for building data-centric applications (HyperCard, FileMaker, App2You, QuickBase, Zoho, Airtable, ...), but to date they have seen limited adoption; we suspect this is because none has achieved a compelling enough combination of naturalness and generality. Instead, many organizations continue to use general-purpose application frameworks such as Rails and Meteor (which demand a depth of technical understanding disproportionate to the problem) or to cobble together tools such as email, spreadsheet and online forms that are easy to use but cannot fully express the application logic (leaving manual work and crude security controls). With Espalier, we hope to offer developers the best of both worlds for low- to medium-complexity data-centric applications.