Based on what characterizes the project, it can be classified according to several main features.

By the pattern of construction of the site
Here there are several categories of web applications:

multi-page (MPA) – the request is sent to the server and the page is completely updated as a result of the response, it is replaced by a new one;
single-page (SPA) – after the request is sent to the server the part of the page that the application consists of is updated without a complete reload
progressive (PWA) – retain their functionality even when working offline due to Internet disconnection.

Depending on which development environment is used, it is possible to get a website template with the specified parameters.

By purpose
Modern web applications can perform many different functions. For example, it can bekorporporativny portals, CRM (customer relationship management), ERP (enterprise resource planning), CMS (content management system), electronic business systems, and so on.

According to the component models used.
In this category there are several varieties:

Absolutely no component models. Often, simple scripting languages help to create a program, which conventionally referred to the style of CGI, although it is a full-fledged application.
With universal component models that are not designed for web applications alone. For example, with the help of COM/ActiveX objects on the Windows platform it was possible to extend the functionality of the web server, to realize this or that business logic.
With specialized component models. An example are servlets and documents, which are universal components in the world of Java development. These components are managed by a special element, the web container.

Depending on which component model is used, optimization of web applications also follows very different principles. Approaches can vary significantly based on functionality and end goals.