Switch offers its functionality through a number of separate applications, each with a distinct function.
Switch server
The Switch server runs in the background, managed and monitored by the Switch Watchdog, to execute flows. It is automatically started and terminated as needed by the Switch designer. If so requested, the Watchdog can continue running after the user quits the designer.
Since it has no user interface there is little to say about the Switch server and Switch Watchdog. Although in fact a reference to Switch often really refers to Switch server (especially in the context of executing flows).
Switch designer
The Switch designer offers a comprehensive user interface to design, activate, and monitor flows. It communicates with and manages the Switch server. The designer and the server must run on the same computer to establish a one-on-one communication.
See Workspace overview for an introduction to the designer.
SwitchScripter
SwitchScripter offers a scripting development environment, that is, it allows creating and testing script packages for use with Switch. The PowerSwitch installer automatically installs SwitchScripter as well. Although there is no technical requirement, SwitchScripter usually runs on the same computer as the designer.
For more information see SwitchScripter, Scripting concepts and Scripting reference.
SwitchClient
SwitchClient is a light-weight desktop application that allows a user on a different computer to submit and monitor jobs. Since it usually runs on a different computer, SwitchClient has its own installer.
For more information see Working with SwitchClient