Basilisk II is an Open Source 68k Macintosh emulator. That is, it enables you to run 68k Mac OS software on you computer. However, you still need a copy of Mac OS 7.x-8.1 and a Macintosh ROM image to use Basilisk II.
Community built
This app is developed in the open by an international community, and released under the GNU General Public License v2.0 or later.