Calendly is an app for scheduling appointments, meetings, and events.
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.
Heroku is a cloud platform as a service (PaaS) supporting several programming languages.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.