When Neos launches, it performs a bootstrap process. The job of this process it to setup the initial world(s) of Neos so user can start interacting with the system. By default, Neos runs the Userspace bootstrap function, which sets up the userspace overlay layer, creates or loads the local home and signs the user in, if he stored his credentials.
The bootstrap function can however be overriden using the -Bootstrap command line argument and providing fully classified path to the class containing the Bootstrap() static function.
Neos will automatically call this function once it's done with its own initialization.
Overriding this function can be used to create various specific Neos' applications, where you want to load or setup a task specific world, bypassing the home experience, userspace and all its functionality altogether.