OneNote as a desktop app, linked as a shared notebook on Sharepoint.
Everything dropped into OneNote can be easily managed through drag+drop. Works offline with synchronization when online. Auto-merges most things at the paragraph level (and has ability to manually merge other stuff). Sharepoint can handle the version control and you can fish older versions of each document out of there if needed.
Much content can be thrown in there (text, emails, screenshots dumped from clipboard, whatever), annotated and/or drawn over, and external files can be dropped right into it or linked via URL.
Using it internally for our team and it's bloody fantastic. The issue we had trying other CMSs (including various types of Wikis, shared folders, vanilla Sharepoint etc) is that they're tedious to use, therefore they don't get used. Our staff love using OneNote so it's being used extensively now. Don't know about its search capability (both OneNote and SP have search but I have no idea how good they are) but we have our folder layout carefully chosen so we can find what we need pretty quickly.
Have even used it recently on a larger project to assign tasks, with milestones and due dates, each one linked to their corresponding Bugzilla ticket that the owners can update as needed. For our small team this worked pretty well.
Not sure about sharing, but some ideas: OneNote can email individual pages as needed, or you could create separate notebooks per client (and let Sharepoint handle the security). Or you could print to PDF and email that out as well. Depends on what your needs are whether this would be a good fit.