We talking about a limited file shredder, or for whole hard drives?
For whole drives, I use KillDisk to zero-write the whole drive 1-3 times before a sale or throwing a faulty one away,
Active@ Kill Disk is a hard drive eraser software for secure formatting of hard drives without any possibility of following data recovery.
www.killdisk.com
Secure Eraser is another for specific files, but I have no personal experience with it.
What is deleted from the hard drive is far from gone. As long as the data is not overwritten, anyone can make it visible again at any time. This is particularly problematic when a computer is resold or given away. Secure Eraser utilizes recognized methods for data deletion and overwrites...
apps.microsoft.com
I am not a Mac-user, but VaultSort seems do everything you need.
VaultSort is the all-in-one solution for Mac users who want to take control of their digital files with military-grade security and intelligent organization.
www.vaultsort.com
Avast, yeah. I used to use both CCleaner and Avast AV, but as Avast has given me problems in the past (a DPC latency issue, to be very technical), and they made CCleaner much more bloated and ad-riddled after the acquisition, I have stopped using both softwares.