ppcrack decrunches all types of Amiga PowerPacker files, including encrypted files. It does not need the password. It can crack the correct decryption key within a few minutes. It also has a dictionary attack for immediate decryption.
ResidualVM, a sister project of ScummVM, is an interpreter for 3D adventure games. Currently, it supports Grim Fandango and Myst3, but some work is being done on supporting Escape from Monkey Island.