The Message Board is a part of the Wii's system software which allows the user to view play time for each individual day, post messages for family and friends, see achievements in certain games (such as obtaining Pro status in Wii Sports), and, if WiiConnect24 is turned on, recieve messages from Nintendo about new channels available for download on the Wii Shop Channel.
In the message board is the Wii's address book, which has the names of your Wii Friends. The address book is very simple with little detail given about your friends. The address book is the main base for things related to WiiMail.
The message board also has a calendar function, which indicates whether a message was recieved on what day.
Every day, the Message Board posts a "Today's Activities" message to the board. It details how much time the user spent using each game or channel, with the exception of Nintendo GameCube games.