Nowadays everything is called a CMS - tools to maintain websites, advanced portals, wiki's, and so on. The requirements for a "CMS" are drastically different for intranets and public websites, however.
Intranets usually have a high level of interaction, lot's of user generated content, different content types, and so on. More users need to be able to login to the system (basically everyone, not just the content editors) with different levels of authorization and different roles in general. Collaboration in general is much more important than with an average "public" CMS based website.
Furthermore you will usually want different types of plugins. Google analytics and SEO are much less important, you'd be more interested in some active user plugin, recent publications, integration with other internal tools (i.e. project management) and possibly exposing other datasources (databases, telephone directories, filesystems with internal documents), and so on.
In my personal experience, Plone is a good choice. It provides most of the above out of the box or through existing extensions and it has excellent integration possibilities with external systems. Cyn.in also provides a somewhat completer plone based solution.
If Plone's too much for you, you could consider some wiki-like system, such as TWiki or MediaWiki