OS X has these features built in, albeit a bit more limited.
To eraser files put them in the trash then from the finder menu select "Secure File Erase"
To wipe free space open /Applications/Utilities/Disk Utility.app, select the hard drive, to to the erase tab, click "eraser free space" and then choose the wipe method.
Two other suggestions to do when using OSX
1) Encrypt Memory
Open System Preferences go to Security turn on Use Secure Virtual Memory
2) Encrypt you home directory
Open System Preferences go to Security and turn on File Vault
(Make sure you turn on "Disable automatic logon" and "require password to wake this computer..." other wise you negate the above to features)