"Maniac Mansion: Day of the Tentacle is a graphical adventure game, originally released in 1993, and published by LucasArts. It is the eighth game to use the SCUMM engine. It was released simultaneously on floppy disk and CD-ROM. Day of the Tentacle was designed by Dave Grossman and Tim Schafer.
The game, a sequel to Maniac Mansion, is focused on Bernard Bernoulli — the only one of the three playable characters that was featured in the first game — and his friends Laverne and Hoagie, as they help Dr. Fred Edison using a time machine to prevent Purple Tentacle from taking over the world. The game utilizes time travel and the effects of changing history as part of the many puzzles to be solved in the game." --Wikipedia.org
A note about the downloads available from above:
This is a Mac-only CD-ROM.
Can be mounted or burned with Toast.