Apache is a free and open-source cross-platform web server software.
Linkedin Sign-In is an authentication system that reduces the burden of login for users, by enabling them to sign in with their Linkedin account.
Twitter is a 'microblogging' system that allows you to send and receive short posts called tweets.
WordPress is a free and open-source content management system written in PHP and paired with a MySQL or MariaDB database. Features include a plugin architecture and a template system.