CAST Extend website
The CAST Extend website is the main "hub" for managing extensions. Extensions can be downloaded (official and custom) and uploaded (custom) in a modern graphical interface accessible in your browser. Access requires registration but is open to all:
CAST Extension Downloader
The CAST Extension Downloader is a software application used in Graphical User Interface (GUI) mode bundled with CAST AIP (from AIP 8.x). As its name suggests, it provides a convenient method for downloading extensions. It is only available with an installation of CAST AIP and cannot be used to upload extensions. You can find out more about this here:
Nuget.exe Command Line Interface (CLI)
Nuget.exe is used to upload extensions in CLI mode, i.e. from a batch file for example. It is only available with an installation of CAST AIP and cannot be used to download extensions. You can find out more about this here.