Sigil is not dead but it's development has slowed considerably to the point it's not being developed very much at this point. The best way I can describe it is Sigil is on life support.
When I took over Sigil from Strahinja I was not planning on taking an active development role. As part of my taking over Sigil my involvement was planned as project management. I was going to manage the web presence, review patches, provide guidance, made releases and at most minor bug fixes. However, that's not what ended up happening. Instead I ended up taking a very active development role. This was never my intention and not something I can continue. I do not plan on ending my affiliation with Sigil; I'm going to go back to what my involvement was supposed to be. Project management.
Since I've been management Sigil there have been about four major contributors (code). These people have been a huge help and a huge benefit and I've very thankful for their help. Ultimately even with all their help I'd estimate half of all code since I took over has been written by me. Due to this and myself not writing code like I was development will slow considerably.
Also, the contributors were never permanent members of the project. This is by their choice. They saw ways Sigil could be improved (mostly something they wanted it to do for their benefit) and helped to make it happen. As they've completed what they were interested in they've left and moved onto other things. Thus Sigil has zero outside contributors as of now. This combined with my decision to focus on project management means there is no one actively developing Sigil at this time.
To help with gaining contributors I've decided to move the project to GitHub. The new source repo is available at https://github.com/user-none/Sigil. This is something I'd been thinking about for some time now. A few reasons behind the change:
Google Code has poor support for working with and merging forks. So much so that most contributors ended up emailing patches instead of wanting to deal with Google Code.
Google Code's issue tracker is terrible. The search feature is useless. The way it displays issues is terrible and hard to understand. The majority of issues posted at least 99% are not real issues but duplicates of issues that are deemed not issues. The most common issue opened is Sigil does not run on OS X 10.6 which for technical reasons is not possible. Sigil not running on an OS version that is not supported, not intended to run on and an OS version that is EOL by the OS vendor is not a bug.
Personally, I believe the issue tracker should be used for code discussion and contribution. That's not happening. So moving to GitHub means it's more likely that that will happen because people will need a GitHub account to open an issue and typically only developers will have a GitHub account. I'm not saying I don't want people reporting issues but when reporting issues means me closing 99% of them as either dup of not supported or not supported makes the issue tracker less than worthless.
Google Code has decided to disable downloads. Existing projects were given an extension but as of next year Google Code can't be used to host binary builds of Sigil. This makes Google Code less useful.
- Calibre moved to GitHub and while Kovid has told me it hasn't increased the number of major contributors it has increased the number of one off contributions. I'm hoping that if calibre moving to GitHub has increased code contributions the same will happen with Sigil.
That's pretty much where Sigil is a this point. I can't say where it will go in the future but my hope is more people will contribute with the move to GitHub and Sigil will continue to grow.