While many in the open-source community do not like Mono on their system as a Microsoft .NET implementation for Linux (and other operating systems), for those interested in this C# compiler and run-time library, Mono 2.8 is now available for download. Mono 2.8 offers up a large number of improvements.
The notable improvements to be found in Mono 2.8 include C# 4.0 support (which is now the default profile), a new generational garbage collector, new frameworks, large performance improvements, the LLVM support is now considered stable, the embedding API hit version 2.0, integrated OpenBSD support, no longer is there a dependence on GLIB, and there is Threadpool exception behavior .NET 2.0.
The new contributed frameworks include ASP.NET 4.0, Parallel Frameworks, System.XAML, System.Dynamic, Managed Extensibility Framework, ASP.NET MVC2, System.Data.Services.Client, WCF Routing, and .NET 4.0's CodeContracts.
The Mono 2.8 announcement can be found on Miguel de Icaza's blog
and more information is to be found in the 2.8 release notes