Digg has a bunch of web servers. One of the problems with running a bunch of web servers is that you sometimes need to get information from each one individually. Or maybe you need to run operations on each one individually. For instance, we use APC to cache configurations and other data. Without restarting Apache we can use Butler to clear configurations from APC or alter APC keys. We also use it to get a bunch of PHP-specific information (e.g. PHP modules and PEAR packages).