It was developed as an online game, but also has offline components.
Note: There are 4 more Myst games after Riven. It's also considerably larger and more difficult than the original Myst. On a side note: Myst's first sequel, Riven, is a 2D-only game. The main difference between realMyst and realMyst: Masterpiece Edition is that the latter uses redone textures of a much higher quality as well as running in a higher screen resolution. This is a noticeable difference if you play the two games.
The main difference between Myst and Myst: Masterpiece Edition is that the former uses an 8-bit color palette, while the latter uses a 24-bit color palette. In the 3D version of Myst, you can explore anywhere. In the 2D versions of Myst, you can only go to certain locations and turn to fixed viewpoints. All version tell the same story, except that the realMyst games have the Rime age not found in the 2D games. The main difference between the two games is that Myst and Myst: Masterpiece Edition are 2D games, while realMyst and realMyst Masterpiece Edition are 3D games.