DiaryPress lets you keep a private diary.
DiaryPress is a plugin designed to allow your blog to operate like a private diary. It will ask you to login in order to access the content. This is handy even if you keep a diary on a local web server such as WAMP as it protects your blog against nosey family and friends. Alternatively if you like to write your diary on the go and keep your diary on an internet accessible server the plugin is fully compatible with all WordPress for mobile applications such as WordPress for iPhone. The plugin is also compatible with the native WordPress e-mail to blog feature.
See installation tab for instructions on how to install.