Word used to offer the ability to save as HTML, which worked fine for mostly text oriented docs. Google Docs offers the ability to download a .ZIP of html and images. I'd wager LibreOffice offers save as html as well, but I can't verify right now. Google Docs is probably most similar to FrontPage as far as WYSIWYG.
Since LM is asking about Frontpage, I'll also mention that this works fine in every version of Word going back to at least Office 2007. You can choose to make a .HTML file or a .MHTML, which is functionally a .zip file with all the file the page needs (e.g. embedded images or fonts) in one.
Google Sites also works, if you just want to toss something online for three or four people. It's specifically nice when integrated with Google Docs.