Free Defragmentation Software for Mac?

I really need to defragment my drive. To say that my Mac is a bit slow would be an understatement. I have heard of the "Macs don't need to defragment" or "They automatically defragment files under 20MB" or "you only do so when your hard drive only has 10% of the space left" and "you only need to defragment in the rarest cases.' But mine does. I ran iDefrag's demo and for some apparent reason my hard drive is in horrible condition. The issue here is that there are a ton of files on my computer greater than 20 MB's, so the hard drive doesn't really automatically manage anything causing major system wide sluggishness on my computer.Vl8btfa_medium

via i.imgur.com

Windows a tool built in, and there are tons for free to download. Do any one of you guys know a free alternative? I seriously do not want to back up my computer, wipe and restore to fix a problem like this. I do not want any down time. This type of fragmentation is inexcusable. I mean, iTunes still opens within one jump in the dock, but boot times and other app load times are rather slow.

So fellow The Verge members do you know any free Defragmentation software?