John Schember, the general maintainer for Sigil, has just posted an update.
This is just a maintenance update, so there aren't any major new features. But the update does add a few dozen bug fixes.
If you've been following this blog for any length of time then you might already know about Sigil, but it never hurts to cover it again. This is an open source Epub editor that is both free to download and free to use. It supports editing both the source code of a file as well as the page view (what you see in a reading app). You can work from any number of file formats including html, rtf, and Epub. But the most important feature, if you ask me, is FlightCheck. This checks to make sure the ebook you're working on meets the Epub spec.