Four games were released between 1999 and 2000 in the Mario Artist series:
Mario Artist: Paint Studio, Mario Artist: Talent Studio, Mario Artist: Communication Kit, and Mario Artist: Polygon Studio.
But there remain 4 more games that were never given a release. Ever. Ever ever.
The Unreleased Games
Mario Artist: Game Maker would have most likely been a game that let players create their own games to save, share, and play later.
Mario Artist: Graphical Message Maker could have been a variety of things. You might have been able to paint messages and send them to other players, but since it has such a vague title it could have been a variety of things.
Mario Artist: Sound Maker would have probably been a game where you could manipulate sounds and sound effects.
Mario Artist: Video Jockey Maker could have been a variety of things. It is not quite certain what the title could mean in terms of gameplay.
It could be presumed that creations could be linked up and shared via The Communication Kit in the same manner as those other games.
To this year/day/month, no playable demos or screenshots have appeared for those games.