Free, Open-Source, and Secure
OpenBSD is a UNIX-like operating system that originated in the mid 1990s. It is widely known for its portability, code correctness, and proactive approach on security. In addition, the folks behind the OpenBSD project maintain other well known security-oriented projects such as OpenSSH and LibreSSL.
OpenBSD 6.6 x64
OpenBSD 6.5 x64
Or, feel free to upload your ISO