What is it?
Messenger Plus! is a freeware add-on for Windows Live Messenger and Skype . The software provides additional functionality to Microsoft's Instant messaging client Windows Live Messenger by adding its own controls to the main interface. These controls affect Messenger's behaviour and appearance, often through additional dialog boxes.
Description of mactrackbarlib.dll from the publisher
“The most popular and respected Windows Live™ Messenger extension, Messenger Plus! has been downloaded by tens of millions of users worldwide, letting users get more from their Instant Messenger experience including plugins, skins, scripts, sounds, emoticons, and more. Messenger Plus! users benefit from tons of exciting features of this freeware that has been enhancing Windows Live™ Messenger since 2001. Messenger Plus! became a market.com brand in July, 2011. Market.com brings together the best in ecommerce, epayments and emarketing solutions, providing all the needed services for a successful ebusiness.”