If you need to view files offline frequently and don't want to use Microsoft's ecosystem, open-source office suites are the most robust solution.
No installation required, high fidelity, official Microsoft rendering. Cons: Requires an internet connection.
If you need an offline tool for your memory stick or local drive, LibreOffice is the premier open-source choice. Its "Impress" application is fully compatible with PowerPoint formats and requires no login or internet connection.
You may still find download links online for "Microsoft PowerPoint Viewer 2010" or "2007."
