This post list some useful resources and sites that offer presentation templates, in different formats like OpenDocument (odp) or PowerPoint (.pptx). Presentation Templates Slidesgo https://slidesgo.com/ Company in Spain. One of the co-founders sold Panoramio to Google. SlidesCarnival https://www.slidescarnival.com/ Free images FlatIcon https://www.flaticon.com/ Freepics This is not really about presentation but for images.
This is a list of some of the free diagraming applications that can be found in the market: Google Docs Draw Free. Commercial. Web-based. https://docs.google.com/drawings/ Dia Diagram Editor Free. Open Source. Desktop application. https://sourceforge.net/projects/dia-installer/ LibreOffice Draw Free. Open source. Desktop Application. https://www.libreoffice.org/discover/draw/ yEd Freeware. Propietary. Java-based Desktop Application. https://www.yworks.com/yed