The Nvu editor was developed between 2004 and 2005 and it's older than the KompoZer and the BlueGriffon editor. If you want to use this kind of editor, then it's better to use the newest products like KompoZer and BlueGifforn or SeaMonkey. More detailed information about the Nvu editor can be found on the wiki page and the editor page.
KompoZerKompozer is a community-driven fork of the the Nvu editor, which means it is the further development of the Nvu editor. The latest version is from the 28th of Febraury, 2010. More details about Kompozer can be found on the wiki page and the editor page.
BlueGriffon is written from scratch based on Mozilla Gecko and XULRunner. The last release is from the 19th of June, this year (2013). The editor is free, but not the plug-ins which can be bought over the web presentation of the editor. What's interesting is that the buttons for those plug-ins are already in the editor, so after clicking on them, a popup window appears and redirects to the plug-in web page, where more information about that plug-in can be found, and besides that, you can add it to the buying basket. More details about this editor can be found on the wiki or editor page.
The older readers are very familiar with the layout of the Mozilla SeaMonkey browser because it still looks like the good old Mozilla Browser, before it was split into Firefox and Thunderbird. The latest release is from the 17th of September this year (2013). Actually I am using SeaMonkey for several web sites, but never used the Composer part of it for editing HTML files. After searching in the web for HTML WYSIWYG editors, I found some links, which I will post here, where the Composer as part of SeaMonkey was listed as editor. More details about SeaMonkey can be found on the wiki and product page.
As I mentioned before, the GUI looks very similar to all four editors that were mentioned here. What I miss in the BlueGriffon and SeaMonkey Composer is the feature where you can see the border of any HTML element, which can be found in the Nvu and KompoZer edior. Here are some links where I got the information from:
Embedded HTML WYSIWYG Editors
Another post that was newly liked on the DZone links section was this link. More links found after searching with the term "free embedded wysiwyg html editor" on the web include:
For the early version of the next articles that I will hopefully write, I will use Mozilla SeaMonkey, because I am using it for other purposes too. I can also recommend BlueGriffon, because all the main functions for editing HTML are free and the project still lives. KompoZer is also a good tool, which is the replacement for the Nvu editor. Actually, you won't notice big differences between them at first. If you are curious now, don't hesitate, try the editors yourself!