Code Igniter is an Open Source Web Application Framework that makes writing kick-ass PHP programs simple as apple pie.
I’ve been playing with Code Igniter for the past two days and must say I’m very impressed with it. It implements the MVC model in a pretty much similar pattern with how Rails does. If you have some experience in one of these framework, getting a project started in the other would be very easy indeed.
I also love how the well the documentation is structured. Quite a lot of open source projects suffer from poor documentation. Thankfully though, this is not the case with Code Igniter. The various information regarding the framework is well organised and partitioned in a manner that makes sense. There are examples galore in the various sections. This helps users to get coding instead of taking on the job scope of a manual editor.
There are numerous helpers, plugins and classes that make Code Igniter a robust framework capable of implementing common (and not so common) features and functions that is required to build a full-fledged web application in a relatively short time. In fact, you can even create a blog in 20 minutes using Code Igniter (video available here)!
Being PHP based, it is also much easier to adopt this framework compared to Rails as almost all web hosting companies support PHP. It is also simple to implement a dev setup on whatever OS platform you happen to use. Basically, if your box can run PHP, then you definitely can run Code Igniter.