Arcana's Experience Broker is a LibDataBroker addon that shows a large amount of experience-related information, including the current amount of experience you have acquired this session, the rate of XP, and the estimated time to level.
This addon requires a LibDataBroker Viewer (such as DockingStation) so the user can see the information.
I wrote this addon because I was accustomed to using FuBar_ExperienceFu and its information display while levelling, especially the distinction between XP gained this Level, and XP gained this Session. Because there was no appropriate LibDataBroker equivalent, I decided to write this as a replacement.
What's a LibDataBroker?
I've received this question a few times, so let me explain what a broker is and why I wrote a data broker addon.
if you've been playing WoW and using addons for some time you might be familiar with addons like TitanPanel or FuBar. These addons place a "panel" at the top of your screen where you can put information like how much gold you have or how much experience you need until you reach the next level.
However, if you wrote a plugin to work with TitanPanel or FuBar, you had to write your addon to work specifically for those systems and ended up having to write two addons (one to support TitanPanel and one to support FuBar). To get around this, some smart people wrote a library called LibDataBroker.
Basically, what the data broker library allows you to do is select the style and look of your UI using a viewer. You can then install the mods that provide data to the viewer (usually called data or data brokers). This provides two benefits. First, the player gets to select what the look and feel of the viewer is. You're no longer limited to something that looks like a bar, for example. Second, the addon author only has to write one addon.
So, what goes on is that you download and install a broker viewer like ChocolateBar, Fortress, DockingStation, or whatever suits the look and feel that you like, and then you install an addon like Arcana's Experience Broker in order to get the information about how much experience you're gaining.