GitHub Desktop is a desktop client for GitHub, a web-based Git repository hosting service. It allows you to work with Git repositories on your local machine, without using the command line. With GitHub Desktop, you can work with Git and GitHub in a more intuitive way, by using a graphical interface.
GitLab is a web-based Git repository manager that provides source code management (SCM), continuous integration, and more. It is similar to GitHub, but is self-hosted, which means that you can run it on your own server, rather than using a cloud-based service. GitLab also provides a desktop client for working with Git repositories, called GitLab Desktop.