Fill a Control with text from the bottom to the top...to mimic a chat window

A simple method would be to add the new messages to the end of the current content, then redisplay it in a GUI box (example in C#):

void OnGUI() { string chatContent = "This is a chat window\nwith\nmultiple\nlines"; string newChatContent = "\nand\neven\nmore\nlines";

 if (newChatContent.Length > 0)
     chatContent += newChatContent;

 GUIStyle style = new GUIStyle();
 GUIStyleState styleState = new GUIStyleState();

 styleState.textColor = Color.cyan;

 style.alignment = TextAnchor.LowerLeft;
 style.normal = styleState;

 GUI.Box(new Rect(0, 0, 400, 200), chatContent, style);

}

Instead of a string for the content you could use a List of strings, which would provide easy addition and removal of lines.

As for a way to enter messages, look into GUI.TextField. See also the GUI Scripting Guide:

http://unity3d.com/support/documentation/Components/GUI%20Scripting%20Guide.html

This is an interesting post about how to make a chat system:

http://forum.unity3d.com/threads/50369-Hep!-Display-what-you-have-entered-in-chat-window