Appears to do duplicate checks via hashing (meaning only exactly the same file), allows for process priority, and uses an easy-to-understand wizard system for filtering files. For a 6 year old beta program, I'm fairly impressed by the clarity and simplicity. I mostly tested it because there seem to be few open source duplicate checkers.
License: GPL v3
Steps: Download the "binaries" zip version and extract
https://sourceforge.net/projects/yadfr/ ... p/download
Supports:
"Windows XP, Windows Vista or Windows Seven systems, 32-bit or 64-bit."
Status: not portable; writes to AppData\Local\