Installed desktop elearning authoring tools need to be downloaded and installed on your computer.
The first advantage of having an app on your desktop and not online is having an exceptional responsiveness that is not dependent on the Internet connection.
Open elearning is a stand-alone product allowing you to build rich and engaging courses on your own.
Having said that, some are bundled with lots of other products such as screen capture tools or image editing software. Installed tools are often feature-rich and can be used to develop highly engaging and interactive courses.