If you just want to try the game before buying, you can download the for the original 2002 game, which includes the "Great Deal" mission. Download Mafia 1 Demo from ModDB
While many sites claim to offer as a "free full version" download, it is not legally available for free as a full game . Most such links are either illegal pirated versions, which may contain malware, or are actually the free demo . mafia-1-free-download-pc-game-full-version
The original game is a paid title owned by 2K Games . To play the full game safely and legally on a modern PC, you have two main options: 1. Purchase the Original Classic (2002) If you just want to try the game