Web application testing services are more complex compared to client-server/desktop application testing services.
A desktop application runs in single memory with both back-end and front-end at one place, whereas a client-server and web application run on two or more machines.
A desktop application has a single user, client-server comprises limited users, whereas a web application can have an unlimited number of users.
A client-server works in a connected mode, whereas a web application runs in a disconnected mode.
Compared to a web application, a client-server has fewer network issues.
A web application is an URL-driven application; however, client-server and desktop applications are not URL-driven.