LibreOffice

LibreOffice is the office suite that replaces Microsoft 365 on the desktop: Writer for documents, Calc for spreadsheets, Impress for slides, plus Draw, Base and Math. It reads and writes .docx, .xlsx and .pptx, and its native format is OpenDocument, which is an actual ISO standard rather than one vendor's file layout. Backed by The Document Foundation, a nonprofit, not a company with a roadmap to monetize you. Licensed under MPL 2.0.

This repository is the C++ core, and it is a read-only mirror; patches go through Gerrit, not pull requests. For everyone who is not contributing, the point is what running it costs, which is nothing. Install it on Windows, macOS or Linux and you are done. No account, no telemetry, no subscription check, and files stay on your disk unless you put them somewhere else. That last part is the real argument in regulated environments and on machines that should not be phoning home.

Free, permanently, at every team size. Solo users and small teams give up almost nothing. Larger organizations should look at Collabora Online for the browser-based collaborative editing and the paid support contract, because that is the gap.

The catch is fidelity and real-time collaboration. A heavily formatted .docx with tracked changes, or an Excel workbook leaning on pivot tables, macros and newer functions, will not always survive the round trip intact. If your workflow means exchanging complex Office files with people who use Office, budget time for cleanup.