Facebook pixel is an analytics tool that allows you to measure the effectiveness of your advertising.
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.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.
Ruby on Rails is a server-side web application framework written in Ruby under the MIT License.
SmtpJS is a free library you can use for sending emails from JavaScript.
VK is a Russian online social media and social networking service.