Krumo is an open source plugin for your programs that is designed as a replacement to print_r() and var_dump(). These functions are used by developers (myself included) to find out what the program is doing. The main problem is that if there is a lot of data to look at the page can get a bit busy.
Krumo solves this by simplifying the output into a more readable format. It tells you the format of the array or object item and any other information that it can gain. It also puts the data into a set of clickable sections so that if you are interested in a particular section of output then you can click on it and see only that section.