ONLYOFFICE Spreadsheet

ONLYOFFICE is an incredibly sleek, highly tactical European disruptor that mathematically bridged the gap between "Open-Source Privacy" and "Cloud Real-Time Collaboration." It engineered a terrifyingly powerful HTML5 canvas engine. It is the absolute weapon of choice for massive secure enterprises who mathematically demand the real-time Google Sheets-style co-editing experience, but absolutely demand to mathematically physically host the entire backend server infrastructure on their own private, air-gapped military servers.