The original Macintosh version of Myst was written in HyperCard.
According to https://news.ycombinator.com/item?id=20549685
Adding useful features, such as uploading those HTML files to a web server, may have been possible but would have required extensions to the language. Plenty of extensions existed, which is how companies like Cyan managed to produce an amazing for the time multimedia game (Myst) on what most people viewed as a stack of programmable black and white index cards.
What extensions did Cyan use for this? How did they work; were they like VBX extension modules for Visual Basic? Did Cyan write them in-house, subcontract them or buy them on the market? What language were they written in?