Desktop software is a one time purchase. It installs on your computer, so you access it there, typically a work computer or laptop. The online system includes all meal plans, however with the desktop program, you buy meal plans as you need them (or create your own).
But, since it is not online, you obviously lose some functions like the online client portal, ability to access on a web browser, messaging, etc. Meal plans and other reports can be printed or saved and sent by email to the client. The desktop tracks weight tests only.