Medusa is a modern interface that allows the creation of virtual machines for Basilisk II and SheepShaver, to be easily manipulated by OSX users. It allows the user to organize files required for emulation, such as disk images and ROM images. It allows using the same files for different environments, it provides tools to stop emulation and helps avoiding data corruption. Medusa is entirely Cocoa-based and won't require any libraries to work. It will not save hidden files in your home directory, but it will use the Applications folder as any OSX application should.
Basilisk II is an Open Source 68k Macintosh emulator: it allows you to run 68k Mac OS software on your computer in a different operating system. However, you still need a copy of Mac OS and a Macintosh ROM image to use Basilisk II. It was developed by Christian Bauer and improved by a large open-source community.
SheepShaver is a PowerPC emulator made forked from Basilisk II. It was once a commercial product developed by Christian Bauer. In 2002, following the commercial decline of Be, SheepShaver was released as an open-source application. Development at that time was driven by Gwenole Beauchesne, who ported the emulator to Windows, Linux and Mac OS X. However, Basilisk II and SheepShaver are not user-friendly and suffer from lack of a practical method to setup.
This is the second of the heavily updated versions of Medusa. It is *NOT* backwards compatible. This version took some user reviews into account.