A Starpack is a special version of a Starkit that combines a Starkit with a Tclkit runtime into a single file.
Starpacks are standalone executables which run out of the box, making them even easier to distribute and use than Starkits. This convenience does introduce a number of trade-offs:
Starpacks only work on the platform for which they have been built
Starpacks cannot modify themselves
Starpacks must be updated as a whole, and are (much) larger than most Starkits
However Starpacks are more convenient for “consumer” platforms such as Windows and Macintosh - the user only has to download a single file.
And they have one other advantage - since the Tclkit is self-contained there is no risk that the application code will be incompatible with future versions of Tcl/Tk.
Note that the contents of Starpacks can be listed and extracted with the SDX utility, since they use the same packaging mechanism as Starkits. The main difference between a Starpack and a Starkit is that the "header" (i.e. the piece of code that is executed on start-up) is a large binary executable file (the Tcl/Tk interpreter) and the files stored inside its VFS include all the standard Tcl/Tk runtime support files.