AngularJS is a JavaScript-based open-source web application framework led by the Angular Team at Google.
Firebase is a Google-backed application development software that enables developers to develop iOS, Android and Web apps.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
PHP is a general-purpose scripting language used for web development.
WhatsApp Business is a free to download app available on Android and iPhone using which businesses can connect with their customers.