Debian is a Linux software which is a free open-source software.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
OpenResty is a web platform based on nginx which can run Lua scripts using its LuaJIT engine.
PHP is a general-purpose scripting language used for web development.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.