Below is a post I added to the Fuel forums on why Fuel differs from other CMS systems.
When I start a project I tend to go for WordPress if a need a general blog / CMS and then if the project is a little more bespoke I will go for CodeIgniter.
Sometimes with a WordPress project it will be 90% CMS and 10% something that isn’t included or there are no plugins for. For this I will create my own plugin.
Then there is the other angle where the bespoke project needs some basic content e.g. about page, links etc.
This is where I feel Fuel really shines. Having all the functionality of CI for the more complex pages is extremely useful and the client need never be involved in this pages. Or if they do need to somehow control these ages such as through adding items to a database it is made very simple through the admin modules.
The modules also make it very quick to create the forms for users to enter and edit the data.
As admin said the others have a larger user base, but I feel this is primarily down to the fact they have been around longer. If you look at Fuel in conjunction with CI then there is actually a vast amount of libraries and contributions as well as documentation.
The only slightly negative thing I have felt so far is that the documentation is not as mature as I would hope. Although the speed and helpfulness of the admin in answering questions has meant that in a short space of time I have got really far in my first Fuel based project.
As I become more knowledgable with Fuel I will be looking to add to the documentation myself, which is exactly how all the other open source projects have evolved into the successes that they are.
I’m sure there will still be times where I use WordPress or a straight CI application, or possibly other frameworks, for projects but I already have two projects in mind that will be based in Fuel and I’m sure many more to follow.
The Fuel website, along with the forum and documentation can be found at http://www.getfuelcms.com/
Or you can download Fuel on GitHub https://github.com/daylightstudio/FUEL-CMS