Ruby is an object-oriented scripting language developed in 1993. It was built with the concept of making programming fun and is characterized by its high flexibility and short, concise code. After almost two decades, Ruby became a popular programming language for web development - many popular web services (Hulu, Airbnb, and others) use it to power the backend services.

It’s an object-oriented language
When a language is object-oriented, it allows multiple related programs to be developed as one large group (i.e., object). This concept was developed to build large-scale software efficiently, which was difficult to do with conventional programming languages.

It’s a scripting language
A generic term for programming languages that make it relatively easy to write and execute programs, such as Ruby, PHP, Python, and JavaScript.

Its main framework is Ruby on Rails
There are many frameworks such as Laravel and CakePHP for PHP, and there are many choices of tools to use, but when it comes to web development with Ruby, most teams use Ruby on Rails. It is not an exaggeration to say that Ruby's popularity was ignited by the introduction of Rails.

Ruby on Rails uses the MVC model in its design, which means that your app is based on a Model (to generate data), a View (to create a look and feel), a Controller (to create functionality), and a Web Development System (to create a web page). 

Therefore, you can divide your development work into two parts, since the display part (View) and the data part (Model, Controller) are separated. This means you can change data components without affecting the view - and vice versa.

Development projects realised with Ruby

Twitter

Twitter, the world's most popular social networking site, was originally developed with "Ruby on Rails". Now it's moving to Scala, a language that runs on top of the JavaVM.
Although Ruby has the disadvantage of being relatively slow, so when the demand for a service increases rapidly, many companies are considering moving to a language with higher processing speed - like Scala or Node.js.

Hulu

Hulu’s MVP was developed in Ruby on Rails, too. It’s one of the biggest streaming services that handle large data volumes on an hourly basis. The team needed a robust but simple framework that can power a complex infrastructure. Ruby, with its simplicity and versatility, naturally was a perfect choice.

Airbnb

The largest accommodation marketplace Airbnb is also developed with Ruby on Rails. The framework is highly suitable for agile development, which is why it is often used for web service development in start-ups and venture companies like these.

Projects where Ruby fits best

• Web application development: simple single-page applications and progressive web applications.
• Social media development: with Ruby on Rails, it is easy to implement user registration and login functions and to manage the database. You can also develop a responsive design that is compatible with smartphones and tablet devices.
• Blog site development: simple sites like blogs don’t require complex back-end tools and code standards, like in static languages. Ruby, with its efficient and dynamic syntax, perfectly covers the needs of blog development.
• Building an e-commerce site: Ruby on Rails has a lot of ready-to-go gems for building online stores. You can easily implement prepared functionality and interface while reusing code fragments.

Projects where Ruby is not the best fit

• Smartphone application and game development: Ruby on Rails has tools such as RubyMotion to convert code to smartphones, so you can develop smartphone applications and social games. However, since Ruby is a language suitable for web development, languages such as Swift, Java, and C# are much better for native app and game development.
• Machine learning and AI development: Ruby has a library called PyCall, and it is not impossible to work on machine learning and AI development. However, it is poorly documented, since most teams prefer to use Python.
• Development that requires high execution speed: Ruby is a so-called scripting language, and as with many scripting languages, it can be slow. This happens because devices need to compile the source code line by line to run the program.

As the demand for services increases, the need for more processing speed is likely to grow, and a move to a different programming language will become an option. This is what happened to Twitter, which was developed in Ruby on Rails when it was first released, and then moved to Scala to achieve better performance.

Summary

Ruby on Rails is very efficient and works great for short term development with a small team. It is well suited for agile and scrum methods of development.
Ruby is a good fit for a small group of developers who want to launch a basic service and then continuously improve it by changing and adding to the specifications to meet the needs of the users.