Apache is a free and open-source cross-platform web server software.
CentOS is a Linux distribution that provides a free, community-supported computing platform functionally compatible with its upstream source, Red Hat Enterprise Linux (RHEL).
Google Sign-In is a secure authentication system that reduces the burden of login for users, by enabling them to sign in with their Google account.
OpenSSL is a software library for applications that secure communications over computer networks against eavesdropping or need to identify the party at the other end.
PHP is a general-purpose scripting language used for web development.