pkgsync is a tool for keeping multiple machines reasonably similar and clean. Packages can either be in a `must be installed', `may be installed' or `must not be installed' list (which is presumed to be distributed separately using a tool such as rdist or cfengine). pkgsync will take care of meeting the demands put down in the lists, and then removing everything that is not in the `must' or `may' list and is not necessary for their operations (as determined by aptitude).