ClickOnce is a Microsoft technology that simplifies deployment of applications by publishing to a website, where the user can install it by clicking a link on a page of that website. After the initial set-up, the developer can update the application with 'one click'.
From msdn
ClickOnce is a deployment technology that enables you to create self-updating Windows-based applications that can be installed and run with minimal user interaction. Visual Studio provides full support for publishing and updating applications deployed with ClickOnce technology if you have developed your projects with Visual Basic and Visual C#. For information about deploying Visual C++ applications, see ClickOnce Deployment for Visual C++ Applications.
ClickOnce deployment overcomes three major issues in deployment:
Difficulties in updating applications. With Microsoft Windows Installer deployment, whenever an application is updated, the user can install an update, an msp file, and apply it to the installed product; with ClickOnce deployment, you can provide updates automatically. Only those parts of the application that have changed are downloaded, and then the full, updated application is reinstalled from a new side-by-side folder.
Impact to the user's computer. With Windows Installer deployment, applications often rely on shared components, with the potential for versioning conflicts; with ClickOnce deployment, each application is self-contained and cannot interfere with other applications.
Security permissions. Windows Installer deployment requires administrative permissions and allows only limited user installation; ClickOnce deployment enables non-administrative users to install and grants only those Code Access Security permissions necessary for the application.
