HTML 5

Things like advanced form elements (sliders, draggables/droppables, sortable lists, etc) and instant client-server messaging (AIM, etc) have been done for a long time in normal programs, but are only now making their way into the web browser through the work of caffeine-powered JavaScript ninjas (see Scriptaculous and Comet). That these kinds of things can be implemented at all is a testament to the flexibility of the HTML/JS/CSS platform, but it also means that the platform needs updating — relying on these complex workarounds is not good.

HTML 5 is happy because in it a lot of these complex things — form elements, plus <audio> and <video> tags, local storage, and more — are built into the browser, so web designers can use simple, semantic tags to do complicated things instead of big, complex JavaScript. Building these things into the platform puts their implementation back into the hands of the OS, which had them figured out decades ago and can do them faster, more consistently, and more reliably. Yay!