BarrelFish, free O/S from Microsoft: Sing#, Sing Sharp, Sing, Sing, Sing!
Sing#, Sing#, let’s all Sing#, oh-la-la, sing, sing, and then bing!
Ok, that’s up there with the 100 BarrelFish title. A connection between the Singularity OS and BarrelFish is the messaging passing concept, but what language will support this easily? Visual Basic? C#? F#? Nope, Sing#. If you are teaching a cranking hard O/S class, then you might want to consider using Sing#, or not.
Take a look at this paper:
Singularity was an O/S that was written mostly using an extension of C# called Sing#. The article states:
Sing# provides support for message-based communication. Using a type and memory safe language gurantees that memory cannot be corrupted and that all failures of the code are explicit and manifest as high-level ex- ceptions (possibly uncaught), not random crashes or failures.
Have fun 
