The webσελίδα Slidesmania has over 200 Google Templates Slides and PowerPoint, which you can download and use for free.
Slidesmania is a site dedicated to providing a wide range of creative and high quality free templates for use in PowerPoint or Google Slides.
The templates in Slidesmania have a variety of styles and are organized into these categories:
• Business topics and standards (Business themes and templates)
• From Educators for Educators
• Celebration
• Education (Educations)
• Formal themes and templates
• Fun themes and templates
• Google slides themes
• Infographics
• Resumes
• Reward systems
• Simple themes and templates
"Edu for Edu" is a special section with templates that are useful for teachers. Looking at the categories you will find templates for resumes, designers, celebrations, to-do lists, games, notebooks, charts and more.
Templates can be saved in Google Slides or PowerPoint or as a PDF or MP4 file. There is a useful tutorial for converting PowerPoint to Keynote for Mac users.
You can see all of this if visit Slidesmania by clicking here. In addition to this site you can find other interesting and free templates from Carnival Slides website. If you search both websites you will definitely find something that matches the job you are doing.