NetScaler is the network appliance and it is available in different types when we talk about the function and features, such as:
Application delivery controller (ADC): This is capable of doing multiple things, such as load balancing of web servers, SQL servers, SharePoint, and many other known services. It can also do content switching and SSL offloading, act as an application firewall, and connect to Cloud.
Gateway: This is also known as Citrix Access Gateway. This appliance is basically used for securing the remote access for the external users connecting to Citrix XenApp or XenDesktop environment.