Diskdeleter - Diskdeleter is data removal software that helps protect your privacy by securely deleting data from your hard drive.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Blancco Drive Eraser - Hard Drive Erasure Software
WizTree - WizTree quickly finds the files and folders using the most space on your hard drive. It scans the MFT (Master File Table) instead of crawling the entire disk which makes it very fast.
CCleaner - CCleaner cleans, speeds up and frees up space on business endpoints.
TreeSize - TreeSize tells you where precious disk space has gone to.