I’m sure others on here can tell you different things about the two, but to me the main difference between MODx and Etomite is that MODx is very modular by design. What this means is that the various parts of the CMS are broken down into parts that can be accessed through a robust API.
For instance, take a look at the RichText Editors in Etomite. The default is FCKEditor and in Etomite it’s embedded in the core code and thus is difficult to change the instance for FCKEditor without modifying the core code. However, in MODx the editors are implemented using a plugin system into the API of the CMS. This allows users and developers alike the ability to create different RTE’s for different purposes without editing the core code one bit.
Another difference is the use of Template Variables, which is something that Etomite doesn’t have. The idea here is to allow users the ability to assign different kinds of variables (text, images, richtext, dates, etc.) to a template that can be used for a variety of purposes. Template Variables when used along side with Snippets allows for an insane amount of power and flexibility that you simply can’t have with Etomite alone. Once you’ve played with Template Variables and understand how to use them you’ll appreciate the power within them.
One of the newest additions to MODx is Modules. Basically, a Module in MODx is more or less just an application that is ran on top of the MODx API. The mix of a module and a couple of snippets would allow you to create something such as a link directory with snippets outputting the link directory inself on the front-end and a module that allows administrators to add, modify, and/or delete links within the manager.
There are many more differences...so many to mention. Some new ones you’ll see very soon in the next TP release (3.3)...but most you’ll see in the up and coming TP4 release. Hope you’ll stick around to see it!
Jeff