WatchXP is a simple addon I started writing while leveling an alt with a friend. Put simply, all it does is draw a little string of text over your experience bar, which shows how far into whatever level somebody else is (currently, only party members that aren't 80). Note that the other person must have this addon loaded for it to work.

Commands: /wxp config -Show the configuration panel

/wxp level <always|diff|never> - Configure the player level option. Always: always show player level after their name; Diff: Only if the player's level is different than yours; Never: Never show player level

/wxp flip -Toggles flipping of text near the end of the bar (Note: may be a little buggy right now)

/wxp toggle -Toggles the displaying of this addon on and off

/wxp version -Shows the current version

/wxp refresh -Force an experience update from all players

/wxp color -Show the text color selection frame

/wxp font <size> <face> -Change the font size and style, where size is a number (12 is default), and face is one of: friz, arial, morpheus, skurri (friz is default)