Mac computers, like Windows, will get cluttered with needless and redundant files over the time, you can speed up a Mac computer running slowly getting rid of the junk. CleanGenius is a free application that will help you erase needless data (mainly logs). After installation a bar chart in the Menu bar will display amount of free disk space left, including attached devices, the app will automatically warn you if you have less than 10% of free disk space left.
A click on the bar chart lets you access CleanGenius preferences from where you can choose to clean Mac OS X system cache, user cache, system logs, user logs, user download folder and trash. After the redundant files have been erased you are told the number of cleaned items and recovered space, CleanGenius can be set up to automatically erase the downloads folder and trash can.
A paid version of this app lets you set up a custom disk space value alarm and eject mounted drives with a single click, it doesn’t seem that the features are worth paying for it, and as for the free app, it doesn’t do a thorough job at cleaning all Mac OS X junk files, there will still be plenty of temporary files left from external applications in your hard drive, but you can use CleanGenius as a hard drive space monitor and for mild junk file cleaning.
If you need a serious Mac OS X junk file cleaner, I would advise you MacPaw CleanMyPC, but it isn’t free.