Lxdream is a Linux-based emulator for the Sega Dreamcast system that is currently under active development. The version number indicates that it is still a little ways to go until a 1.0 version but quite a number of demos and even some games are running. The latest versions boasts OSX support!

This is what the authors' wrote on the release:
Change of plans - because svn looks likely to become unstable for a little bit with recent work (MMU changes are fairly invasive, and there is quite a performance penalty that I have not optimized away yet), I am releasing 0.8.2 as it is now (without TLB) for the benefit of those who need the fixes since 0.8.1.
Note: There are no significant changes to the emulation (ie no change to compatibility) - If 0.8.1 runs properly for you, you do not need 0.8.2

Changes from 0.8.1

* x86-64 architecture support
* Preliminary Mac OS X support
* Pbuffer support (to support OpenGL drivers without EXT_framebuffer_object)
* Support for more recent CDI and NRG image file versions
* Minor bugfixes
- The website
- A compatibility list