DGen is Sega Mega Drive emulator originally written by Dave. It runs on many operating systems including Microsoft Windows, Linux and the BSDs. Versions until 1.04a were released for DOS, but these never had sound support. Since then, a newer version using SDL as a backend has been released, named DGen/SDL. There is also a PlayStation Portable release called Syn-Z 
DGen/SDL is actively maintained by Zamaz and a hanful of other developers. Since the demise legacy Dgen, the newer Dgen/SDL has seen the addition of video filters, a vi-like command interface, region autoselection and a m68k debugger. Releases occur roughly twice a year.
Downloads can be found on the Dgen/SDL Sourceforge page.