OpenOffice Open source office suite - free download - presentation software can be saved as PowerPoint.
Google Presentations AKA Slides - Use your school Google Account and gain access to free, online, web-based productivity software. Google Presentations have features similar to PowerPoint. You can even upload PowerPoint, insert PowerPoint into Google Presentations, and embed Google Presentations on various websites.
Keynote - Apple's Presentation Software, available on Mac, iPad and iPhone.
PowerPoint - Microsoft's Presentation Software, available on PC and Mac.
Canva - Web Based tool (free and paid versions available)