You can easily tell from a simple search on Google (or your favorite search engine) that the term "FrontPage killer" gets used a lot in reference to many different web site creation programs. This terms has been used by supporters of products like Macromedia (whooops! Adobe) Dreamweaver, Adobe GoLive, and so on.
In my most recent search using this term, I came across a free application called NVU (pronounced "n-view" and stands for "new view"). Although I have not used this application yet, it has been touted by many bloggers as the standard "FrontPage killer". (Just from reviewing their web site, it appeared to be pretty exciting.)
However, I must confess that the first time I heard the term "FrontPage killer", it was by a Microsoft Employee in reference to an upcoming replacement for Microsoft FrontPage. (However, it was made clear that they were not allowed to really call it that.)
When I was getting a new download of MS SQL Server Books Online today, I noticed an ad on the MS web site for something called "Microsoft Expression Web". This immediately raised a red flag with me, reminding me of the statement above. So, I clicked on it like a drone and saw the supposed "FrontPage killer". Here is a link to it. Let me know how you like/dislike it.