The command is CONTIG (also available in 64-bit as CONTIG64), is a Sysinternals:
https://docs.microsoft.com/en-us/sysinternals/downloads/contig
It defrags, and does it very well. It does it file by file. Here’s a command probably suitable for background operation on a whole C drive, on a 64-bit machine, quiet mode:
start /LOW contig64 -s -q C:\*