No, El Dorado is pretty much a package. Of course, you could take it and customize it as much as you like. If you only wanted to use the forum, it would be easy to disable the rest of the functionality. If you need something more modular, take a look at adva_cms. They seem to be doing some very interesting work:
http://github.com/svenfuchs/adva_cms/tree/master
Other similar offerings would include:
http://lovdbyless.com/
http://missingmethod.brunobornsztein.com/projec...
http://github.com/radiant/radiant/tree/master
For just a forum, Beast is very popular:
And in PHP there's a lot of modular stuff:
http://drupal.org/
http://wordpress.org/
http://www.movabletype.com/products/community-s...
Hopefully, you can find a use for El Dorado, though! :)