The new GIANT website can be found at https://giant.cce.af.mil. You will get an alert about an untrusted certificate if you do not have the DoD CA certificates installed on your machine. Please see https://public.cyber.mil/installroot_5-4 for installation instructions.
This site is still secure despite your browser providing warnings. In your browser, you can click 'Advanced' to gain access to a 'Proceed to giant.cce.af.mil (unsafe)' link if you are unable to install the DoD CA certificates.