Keikai is described as 'is the only Web Spreadsheet designed and architected for big data — and is the fastest web spreadsheet regardless of size. Other advanced features include embeddable in your Web Apps, providing true Excel experiences and more' and is a Spreadsheet in the Office & Productivity category. There are more than 25 alternatives to Keikai for a variety of platforms, including Windows, Mac, Online / Web-based, Linux and Android. The best alternative is LibreOffice, which is both free and Open Source. Other great apps like Keikai are LibreOffice - Calc (Free, Open Source), Microsoft Office Suite (Paid), Apache OpenOffice (Free, Open Source) and Microsoft Office Excel (Paid).
LibreOffice is a free and open-source office suite that is compatible with other major office suites, and is available on all operating systems. It is an independently-developed version of the OpenOffice.org suite.
LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.org Calc, professional data miners and number crunchers will appreciate its comprehensive range of advanced functions.
Airtable is the easy but powerful organizational tool that works exactly the way you want. It's as fast and flexible as a spreadsheet, but offers a refreshingly clean, modern way to organize and collaborate on everything.
Office Online is an online office suite offered by Microsoft, which allows users an easy way to access, view, create and edit documents using lightweight, web browser-based versions of Microsoft Office applications: