Informat is an add-on that comes bundled with the Auctioneer and AuctioneerSuite add-on, but can be installed and enabled independently if desired.
This add-on extents the normal mouse-over item tool-tip windows to display extra detailed information at the bottom of the tool-tip.
This is especially useful to see the vendor sell price of an item, or what use an item has if you do not recognise it. For example it will tell you if an item can be used for a trade skill like tailoring or leather-working etc.
The Stubby add-on (which also comes bundled Auctioneer and AuctioneerSuite) must also be installed and enabled in order for this add-on to function.