MacJanitor is a free Mac OS X system maintenance tool. It is a very simple app that serves a very specific function. According to the description on their website, Mac OS X computers are designed to run constantly, and most automatic system maintenance tasks are set to be carried out late at night. So, users who don't leave their computers on over night, won't ever have those maintenance tasks done. The application solves this problem by letting you carry out those operations manually.
When you run the application, you have to click on the little "lock" icon to gain administrator privileges. This will bring a window up where you have to type in your user password. Once that is done, you can click on the daily, weekly, and monthly buttons to carry out those system maintenance operations. Or, you can click on "all tasks" and do them all at once. When you click on one of them, the application will show a text log on the main screen that shows exactly what is done. The information is a bit technical, though.
In my testing, doing all the tasks took a little under 20 seconds. I really didn't notice any change in my system in terms of speed. But different users will probably get different results.