File Format
The foundation everything else is built on.
The file format is the most important decision in an office suite. It determines what the product can do, how far it can scale, and what it will never be able to support no matter how many engineers you throw at it. Legacy formats carry 30 years of constraints, and every product built on top of them inherits those constraints whether they realize it or not.
We built a new format because the foundation is the moat. Not the UI, not the feature list, not the integrations. The format. It is the one decision that is nearly impossible to change later, and the one decision that defines the ceiling for everything you build on top of it. We chose to start there.