Well this is some amazing news that has been a long time coming. You can take your Flash apps and run them without Flash, and take your Silverlight apps and (almost) run them without Silverlight.
The Mozilla Project "Shumway" has been a long time coming (as long ago as 2012, but it's now ready to be looked at more deeply).
Chris Peterson, a Program Manager on the Mozilla Shumway says:
"Shumway is in a race to stay relevant as Flash fades from the web, but there will always be a long-tail of Flash content that would/will be lost when Adobe or browsers stop supporting the Flash plugin."
Think about that. We've all largely got "Evergreen Browsers" now that update themselves as often as weekly, but sometimes it feels like Adobe Flash is being attacked daily, so we're told to update that as well. Flash itself has more than fallen from grace, as Chris points out, it's fading from the web itself. Fast forward a year or so when there is no more Flash installed, but there's still Flash on the web. Enter Shumway - it's a renderer for SWF (Flash files) without native code! Shumway literally.
Why is it called Shumway? Again, Chris:
"The name "Shumway" is derived from "Gordon Shumway", the actual name of the TV character ALF: Flash -> Flash Gordon -> Gordon Shumway -> Shumway."
To be clear, there are significant architectural differences between these two projects. Shumway reads the binary SWF format and tries to Be Flash, while Fayde is reimagining, if you will, that takes the Silverlight concepts of ViewModels and Views in XAML and adds TypeScript (a comfortable language for the C#-familiar) with the result rendered on a Canvas. It's not a Silverlight Emulator, it's a Silverlight-like implementation and app development pattern for HTML5. It's open source, and they are looking for participation, so head over and get involved! Fayde may be the Silverlight migration strategy you've been looking for.
Aside: From my perspective, it's not unreasonable to imagine taking something like JSIL (listen to my podcast on this amazing project) or a similar IL->JS system and combine it with Fayde to somehow run XAPs as well.
Have a lovely day and enjoy today's Open Web.