Battery Guru is a menubar application that tracks laptop battery health. Its menu icon displays the number of milliampere-hours currently being used; when clicked, it displays additional information about the battery: the current capacity, the original capacity, the number of charge cycles the battery has undergone, the battery's date of manufacture, the temperature in Celsius and Fahrenheit, and the current charge. It also provides links to the app's App Store page and the developer's website.
And that in its entirety, is what the app does. There are no nifty features, graphical interfaces, or customizable options to this app. It's simply good for keeping track of how much electrical charge you're drawing at any given time, with some additional statistics about battery health displayed upon click. It's of limited use to the average user, since it does not translate this number into an estimated expenditure time, nor does it update the statistics very rapidly. But the information does seem accurate, so it could be useful for the right task.
Sam's Protip: really the only feature this free battery monitor has over others is its display of current mAh in the menu bar, and it lacks many other possible features. Give it a miss unless you know what you're doing.