This is a humble programmer's text editor. To be honest, it's not a lot. It doesn't feature any fancy new innovations. It's simply a text editor, meant primarily for programmers.
So why does it exist? It exists to fit the needs of one particular programmer. For this programmer, Xcode is too clunky for small tasks or casual projects. Smultron 3 doesn't support any Lion features like versions, and Smultron 4 was the victim of a terrible new user interface. BBEdit is overpriced, doesn't support versions, and just doesn't "feel right". To put it simply, it exists because this one particular programmer wanted the perfect editor for him. And so he began creating it.
We aren't going to claim that this app has any more features than the others, or even that it's better. However, for this programmer, it's the right app for him. At the risk of being cliché, we'll leave you with this: CodeX probably isn't the right text editor for everyone, but it might just be the right text editor for you.