Workshop:

 
Basics
 
Shell
 
Ghost
 
Balloon
 
 
Index
On desktop a character, usually 2 (many more displayed rarely) which talk in a speech bubble, is shown.
Nice. And what is the whole thing?
Imagine that the desktop is a kind of stage. Appearance: your Ghost!
It could also be viewed as a "Speakers Corner"* on desktop.

Many ghost authors design their ghosts exactly this way.
OnFirstBoot: "Huh, I'm here on desktop, and what should I do here?"
These are the more timidly designed ones, which also say something similar to end: "May I go now?"
At the other end of self-confidence coefficient scale, there is also true ramping.  (nowadays: true Trumping)
Everything from the respective Ghostautor so built. It is only a faked artificial intelligence.
Depending on skills (and workload), however, it can look almost like a real one.
Do not be shy, most of the Ghosts do not come close to this range.
(Also my own ghosts are still expandable)

There is a broad spectrum of topics.
GHOST TOWN lists for talk:   sharp tongue, heartwarming, nonsense, comedy, depressive
View of the world:   fantasy, SF, robots, realistic, monsters, ghosts, occultism, death, devils, angels, animals, shop
So, is it ALL? Yes actually. What, restrictions?
I want to put it this way:
Design your texts so that you do not have a letter from prosecutor's office in mailbox!
So do with pictures (copyright?).

*
Scripts are split into 'events' and 'random talk'.
Every section of 'random talk' works like a comic strip (one line, 3 or 4 pictures).
Can be expanded to a 1 or 2 sider, but please don't write novels.
Some ghosts have a nearly endless 'first boot' part - annoying!
To introduce your characters the long way, you can better use a menu point like "Tell something about you" or else - THX