Busybox ported to Windows. Can be compiled for both 32-bit and 64-bit Windows. Includes shells. Can be cross-compiled from a Linux box. Make sure that you look at the README.md file, not the regular README for build documentation.
An open source utility for Windows (32 and 64 bit) that will securely erase files and directories on a Windows machine, in addition to scrubbing free space and OS-related temporary files that could leak information. It can even wipe an entire system if you need it.