When users upload files - there are some documents which may need to be edited - so if there's a plugin or an extension which is within AC itself that allow for online editing / or translation of the file before it gets published on the site - that would facilitate collaboration and teamwork.
Like Xinha http://xinha.webfactional.com/ or HTMLArea http://www.htmlarea.com/
Visual editor is available in activeCollab 1.0, but for general use (ticket descriptions, comments, page content etc). However, you cannot upload a Word document as and edit it directly from activeCollab. You can download it, edit it in Word and upload it as a revision.