Linkover loads the link in the background when you hover it, gets all info about it and shows a nice tooltip over the link. It contains page title, thumbnail and short description for many pages over the internet. It's a great approach to preview links before visiting them.
Linkover was created as a solution to the problem when some sites truncate long titles of the link titles, putting the obnoxious \"...\" at the end. In some cases it can totally prevent you from understanding the content of the page without clicking it. It could become especially painful on websites like Google Search and YouTube.
Linkover provides several options to prevent unwanted link loading, including domain blacklist, whitelist, and requirement of modifier key pressed (enabled by default). It can also load link info on long left click instead of on hover.