4. C'est La Vie Silverlight
There was a time when Microsoft's Silverlight positioned itself against Adobe as a more efficient alternative to Adobe Flash. But the interactive Windows add-on, Silverlight, never caught fire. Worse, it still doesn't work on the Windows Store (a.k.a. Metro) or Microsoft's own Windows Phone. Global Knowledge said Silverlight's days are numbered, along with any developer that isn't becoming an expert in its successor, HTML5.