If you are looking for a breakdown of what this version is and why it's still being searched for, here is a quick piece on the "Retail" legacy of Project 2016. The Classic Powerhouse: Microsoft Project 2016 Professional
Unlike Volume Licensing (used by large corporations), the Retail version was designed for individual purchase. It doesn't require a constant internet connection to validate your license, making it a favorite for "offline" setups. Microsoft Project 2016 Professional Retail Free...
Tools like ProjectLibre or GanttProject offer similar Gantt chart functionality for free without the licensing headaches. If you are looking for a breakdown of
Unofficial "cracked" versions often come bundled with malware or security vulnerabilities. these are typically unauthorized distributions.
While sites like iGetIntoPC often list "free" or "full offline" versions, these are typically unauthorized distributions.