Steamtools is a Software to obtain games and or DLC's through Lua and Manifest files as well as ST files. The games appear directly in your Steam Library, meaning things such as Achievements are Supported. It is similar to owning the game but instead you just... haven't bought it. It works perfectly except for a few minor disadvantages, such as no online features by default and a few games not working due to DRM, AntiCheats and Launchers (e.g Rockstar).