I used MODx as the base for a web-based translation termbase with client access to their own termbases. It involved a module to allow my client to upload either csv or plain-text files with terms in up to four languages into a custom database table. I made it Ajax-driven so it can be edited online (see the demo on my site,
http://www.sottwell.com/database-module.html and use the guest login to see the module itself)
For the front end, when a client logs in they are automatically sent to a page (in their selected language) that gives them the option to browse their termbase or search. This is accomplished with a snippet, which pretty much just does an include() of the php files needed to provide the functionality.
This was a fairly simple application. But it demonstrates how you can use the MODx framework to do anything you want. Use modules to add back-end functionality, and snippets and plugins to provide front-end functionality. Or, like NewsManager, you can use the front-end for everything. Personally, I prefer to keep all management stuff in the Manager.