Dropbox is a cloud storage service that allows users to store their data on remote servers. The remote servers store files durably and securely, and these files are accessible anywhere with an Internet connection.

Instagram is a photo and video-sharing social media platform that allows users to share their creations with others. The original poster can set the visibility of these posts (photos/videos) to private or public. Posts can be liked and commented on by users. Users can follow and see the news feeds of other users (a collection of posts from the users they are following).

Whenever you open Facebook, the News Feed is the first service that you encounter. It is a continually updating service consisting of posts, photos, videos, comments, and activities of the people and pages you follow. Every Social media platform, such as LinkedIn, Twitter, Youtube, Instagram, etc., has a News Feed service, the main landing page, and displays real-time updates. Many companies also use Social Media platforms for advertising their products and using Machine Learning to offer customized and relevant advertisements to the user to increase their profits. Over the past few years, social media platform such as Facebook has scaled tremendously. News Feed is a vital component of Facebook as it directly affects user engagement and constant interaction. Hence Facebook teams are highly concerned about every use case and aimed to provide real-time services. Without much, let's look into the critical requirement of the Facebook News Feed service.

Twitter is a social media platform where users may post and interact with “tweets.” Users submit and engage with “tweets” on Twitter, a microblogging and social networking site. Users can subscribe to other users’ feeds and receive tweet notifications from those they follow. Tweets are almost 140–280 character communications.

In today’s world, notification services are widely employed in almost every product. They’re helpful if you’d like to be alerted of a price change or availability of a product you’re interested in, or if you’d want to be told if a new job specification for a job search criterion you’ve provided becomes available.

Design a Yelp like service, where users can search for nearby places like restaurants, theaters, or shopping malls, etc., and can also add/view reviews of places.