Web apps are developed using a combination of front-end and back-end technologies. 

Front-end technologies include HTML, CSS, and JavaScript, which are responsible for creating the user interface and interactivity. Back-end technologies include programming languages like Python, Ruby, or JavaScript (Node.js), as well as frameworks like Django, Ruby on Rails, or Express.js. 

Databases such as MySQL, PostgreSQL, or MongoDB are used to store and retrieve data. Additionally, web servers, such as Apache or Nginx, and deployment platforms like Heroku or AWS, are utilized for hosting and deploying web apps.