defragging is a part of the NTFS file system, which is what Windows uses.
With linux, you have multiple choices for file systems, but most use Ext3/4. Regardless of which one you choose, none of them put files in sequential order like NTFS, there is no need to defrag a hard drive.
The microsoft utility you are thinking of goes through and cleans up temporary files. It empties out the recycle bin, deletes browser cache, things like that.
Once again, these things aren't really needed in linux. You could clear out your browser cache via the browser's utility if you wished, which might help make it fun faster, but won't really affect the system as a whole. /tmp (where temporary files are stored) is generally cleaned out by the OS without needing any user intervention.
Linux handles RAM differently from Windows fundamentally and it's file systems are very different. There are just some of the reasons that you won't find a linux version of these utilities.
There is a Sabayon specific command to delete the downloaded entropy packageshttp://wiki.sabayon.org/index.php?title ... d_packages
But all that will do is free up some hard drive space. It won't really have any impact on performance unless you are running out of hard drive space.