At this week's TechEd conference, Microsoft announced that they are adding HTML5 support to Visual Studio LightSwitch, the tool intended to simplify the development of custom database-driven business applications.
The Silverlight client will remain the default target for LightSwitch applications. Microsoft says that the current primary focus for HTML5 applications is mobile optimization and touch functionality. A likely scenario would be a full-featured desktop client running on Silverlight, with an HTML5 mobile companion application. LightSwitch allows for these to be built side-by-side in one project.
The LightSwitch HTML5 client is not yet available, but it's expected soon. It will be available for download from the LightSwitch Developer Center.