This may exist, but I couldn't find it. How about the ability to place a sign and then a player could walk up to it and hit it and an expanded text box would pop up with the full text. Maybe allow up to 200 characters or something. This could be very useful for conveying information to people such as information about the server in the spawn for new players.
This would require a client mod. You could do it so when the player presses a sign it'll send them something in chat. But you can't do it so an actual box comes up.
