Simple addon that does a few different things.
First, it provides a resettable earned XP counter. It works like a car's tripometer. You click the reset button when you want it set to zero, and it'll tally up all earned XP after that (including from quests...).
Second, it provides easy to read "bar" counts for your trip, remaining XP and rested XP. Bar in this case being equivalent to "bubble" or 1/20th of your current level's needed XP.
Third, provides a display on the unit frames for your party that displays the number of bars they have remaining, provided they also have the addon.
Slash commands:
"/xpom reset" - Resets the counter.
"/xpom lock" - Locks the display window in place, or unlocks it if it's already locked.
"/xpom show" - Toggles showing "earned xp" notices.