It's a place where the database doesn't really have a good option. There's no "Presentations" option in the category list for a reason. The closest we have is "Office Suites," which is a short list: https://www.portablefreeware.com/index.php?sc=96.
The closest program I have is Notzy (which borders on portable) but it hasn't been in development for some time.
Anyway, ideal would be something that's not web-based but I'm keen to find out what people are actually using.
- ONLYOFFICE isn't bad but still insists on chasing the never-stable Microsoft Office format for all it's files (just check out their changelog for all the effort they're putting into DOCX and XLSX compatibility). I'm not excited about saving files to an unstable format, but maybe I'm just being obstinate.
- FreeOffice does have a presentation editor ... but I get the sense that it's mostly the same program from 10 years ago.
- PhotoFilmStrip - limited feature set versus similar tools and hasn't been updated in some time but it is open source and portable
- Marp - Markdown for presentations