Building applications on spreadsheets

This may confuse you, as spreadsheet is already an application. Let me put it in this way.

You might be an analyst, you want to build a DCF model. You are designing a game, you want to do some math. Or maybe you just want to play Go using grid.

More than extension

Excel already has many extensions. But we want applications. Application has their own managable states which users' operations can hardly affect.