If you're looking for a free and open-source alternative, you can consider various Linux distributions (e.g., Ubuntu, Linux Mint, Fedora) that offer similar functionality to Windows.

If you're looking to install a new operating system, I recommend considering a newer version of Windows, such as Windows 10 or Windows 11. These versions receive ongoing support, security updates, and feature enhancements.

You can buy Windows 7 Ultimate 64-bit from Microsoft's official website or other authorized retailers. This will ensure you receive a legitimate, licensed copy with support and updates.

To help you with your original query, I'll provide some general text: