A few months prior to Chrono Trigger‘s market release, a beta version was given to magazine reviewers and game stores. An unfinished build of the game, it contains numerous differences from the final version, such as unused music tracks and a location called “Singing Mountain”. Curious fans later explored the ROM image through various methods, discovering two unused world map character sprites and presumed additional sprites for certain non-player characters. This has led some to rumor that an eighth playable character exists or was intended for play, but there is no evidence to this claim. [Info from Wikipedia]
As we can read from the translation of the Seiken Densetsu Music Complete Book:
Soon enough, it became the time in which the Super Famicom was completed and released. During that time, we were still seeking a higher capacity media for our games, and upon getting word from Nintendo that they were developing a CD-ROM adapter for the Super Famicom, we decided to start a project in a different direction from Final Fantasy IV, which at the time was in the middle of development and was touted as a next-generation RPG fitting the large storage capacity the new cartridges had. The development codename for the new project was Maru Island, and we were making it as a collaboration work with Akira Toriyama-sensei after we established contact through Shueisha. I frequently ran back to the office just to receive and look at the screen mock-ups that Toriyama-sensei did in the initial stages of the project.
Despite that, the CD-ROM adapter was never completed. Once everyone learned that the CD-ROM adapter was never going to see a release, they decided to abandon everything that had been planned for development since the very start, including Toriyama-sensei’s contributions, and decided to revise the project in order to make it release into a ROM cassette. We said that we would wait for the CD-ROM to make a collaboration project with Toriyama-sensei, but when it was revised, it actually became an entirely different project with an entirely different direction. That was what later on was completed into the game we know as Chrono Trigger.