BleachBit

Open-source and free, with the one feature that actually matters for privacy here: shredding files and wiping free space so deleted data doesn’t linger. That focus is its strength and its limit, since it’s a cleaner that can erase, not a polished tune-up suite. The interface is utilitarian and it’ll happily let you delete something you wanted if you tick the wrong box. Pick it when secure deletion is the point, not when you want a pretty Mac optimizer.