Microsoft Office Excel - Microsoft Office Excel is a commercial spreadsheet application.
ReqRes - A hosted REST-API ready to respond to your AJAX requests.
LibreOffice - Calc - LibreOffice Calc is the spreadsheet program you've always needed. A fork of OpenOffice.
JSON Placeholder - JSON Placeholder is a modern platform that provides you online REST API, which you can instantly use whenever you need any fake data.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
JSON Server - Get a full fake REST API with zero coding in less than 30 seconds. For front-end developers who need a quick back-end for prototyping and mocking