Gemini II is a telescope goto computer, a piece of hardware to control a telescope mount...
the Sky is a piece of software (basically called "a planetarium program") ...which is used to control goto computer mounts, such as the Gemini (or others).
Gemini II has inbuilt catalogues of objects for goto targeting (via the handset) and you can update and change these or use
Gemini ASCOM or such like to control the mount. So in theory you don't need a planetarium program to run the mount.
You can also use the mentioned Planetarium programs to control the Gemini mount (or other computerised mounts)...such as "the sky". Planetarium programs are common and liked as it visually represents objects to see....and much more.
But you cannot compare a Gemini II to The Sky as they 2 items perform differing tasks.