In a thread on the board-discuss section, @ohallot listed a number of features LibreOffice has but almost nobody knows about:
and possibly others.
I know about Hybrid PDFs: That how you can export a PDF which also contains the original document, which you can then open in LibreOffice for continued editing and also in PDF viewers for viewing like a regular PDF. This YouTube video demonstrates that flow.
But what about the other features? What are they? The public thirsts for enlightenment! 
Hi Eyal,
Thanks for highlighting these! I’ll start to promote them on our social media channels, Reddit etc. Starting with the first one you listed, TSCP classification:
Everyone is free to add more lesser-known features that deserve a mention, and we’ll do some promotion 
Cheers,
Mike
Actually, that particular feature is not quite attractive. I think I would probably appreciate LO declaring lack of support for state-secret-stuff. 
… this goes hand-in-spiked-glove together with the “promotion of sovereignty” line.
I don’t know how “secret” it is but I’m a big fan of how LO can insert QR codes out of the box with Insert > OLE Object > QR and Barcode.
Especially since there are many online “free QR code generators” that actually use a redirect in the middle, and later on ask you to pay to keep the redirect alive… Absolute scammers, defeating the purpose of QR codes.
Something to advertise!
Well, not literally secret, just hard-to-notice/easy-to-miss; I’ve added quotation marks.
maybe in the couple of hundreds Tip of the day / Tip of the Day
listed here : tipoftheday.hrc (revision 2038d4a4) - OpenGrok cross reference for /core/cui/inc/tipoftheday.hrc
Also not a big secret, but my friends and I think the features of Draw to edit pdfs directly are awesome and not broadly known.
This feature is near and dear to my heart, and I spoke about LibreOffice as a PDF editor last year at our annual conference…
Interestingly, LO is relatively well-known as one of the most readly-available ways to edit your PDF in Linux.
What’s unfortunate, however, that the PDF importing is still quite poor, with no reconstruction of paragraphs, styles, etc. and widely divergent reproduction of content. See slide 4 in my slide deck for an example, as well as bug 32249.
You already know that you can join several adjacent lines (text box) into a larger text box and do some basic text reflow, right?
Another well kept secret? Not yet a PDF editor but handy nevertheless.
Cheers
Olivier