Yabause is a Sega Saturn emulator create under the GNU license. It currently runs on FreeBSD, GNU/Linux, Mac OS X, Windows, Dreamcast, PSP and Wii.
It's still in development but it's quite stable and support booting BIOS and some games using Saturn CDs or ISO files.
Here's changelog:
+ Working Netlink emulation over LAN/internet
+ CD audio emulation fixes
+ Support for mdf/mds (version 1) dumps
+ CD+G
+ GDB stub
+ Saturn mouse and 3D control pad
+ Awesome new SH2 debugging features
+ More user-friendly interface
+ At least 0.0.1 more than any previous version
+ And of course, better overall emulation
Visit project website for for further information and latest files.