Aspose PPTX Viewer App is a free and easy-to-use online presentation viewer or reader. You get to open your presentation from any computer (Windows, macOS) or smartphone (Android, iOS). Simply upload your file. No software installation is needed.
Cost / License
- Free
- Open Source (MIT)
Platforms
- Online
United States
Best alternatives are 
LibreOffice - Impress
9 alternativesLibreOffice - Impress