Private is a very simple node access module that gives each node a 'private' checkbox. If it's set, it can only be seen by the node author, or users with the 'see all private nodes' permission. It's most useful on small sites with limited needs, like single user blogs that want to hide a few posts from the general public without the overhead of a comprehensive access management module.
Per-content type defaults, Actions integration, Views integration are also part of the 6.x version of Private module. Building views of private content, or performing bulk flagging of nodes as private or public, can simplify life for administrators as well as end users.