: "G3D" is a common file extension for 3D models or engine data. This could be a community-made collection of assets (like mods for a game like Gothic or Minecraft ) optimized for Radeon hardware.
Given the name, it likely belongs to one of three categories:
: You can use tools like 7-Zip or WinRAR to "Open Archive" instead of "Extract." This lets you browse the file list without running anything.