People write (<a href="http://www.julmar.com/blog/mark/PermaLink,guid,3670d081-0276-48e6-b97d-1b644093b52e.aspx" rel="nofollow">http://www.julmar.com/blog/mark/PermaLink,guid,3670d081-0276...</a>) that even .NET itself has a similar kind of GC (partially concurrent, only address fixup stops the world). Unfortunately I can't check how it compares to Singularity.