Indeed there may be more of these CMS-lite tools than there are CMS themselves. Many Wiki sites have surpassed 10,000 downloads and thousands of registered users.
See the Information's Architect's Wiki for an example of how wikis are used, with a lot of valuable information for designing a CMS. An even better wiki is Simon Willison's companion wiki to the CSS-Discuss mailing list.
Also see the CMS Wiki where you can contribute to a knowledge base for Content Management Systems.