Basilisk II is an Open Source 68k Macintosh emulator. That is, it enables you to run 68k MacOS software on you computer, even if you are using a different operating system. However, you still need a copy of MacOS and a Macintosh ROM image to use Basilisk II.
Thanks to http://www.dcemu.co.uk for the news and the hint for the next few following ones.
AEP-Emu (DE/EN)
DMG Page (DE)
Indie Retro News (EN)
Retroguru (EN)