Most likely the answer you're looking for is the HTML5 stack. This allows for rich animation and manipulation of text and multimedia through Canvas, CSS3 transforms, and JavaScript. HTML5 also has built in support for multimedia through <audio>
and <video>
tags. Multimedia can also be manipulated and analyzed through new API calls available in JavaScript. There are also a host of JavaScript libraries like RaphaelJS for creation of interactive vector graphics.
http://raphaeljs.com/
Since you are interested in creating multimedia presentations I would recommend checking out HTML5Wow which is essentially a presentation on the capabilities of HTML5, made with HTML5.
http://www.htmlfivewow.com/slide1
There is also capability for 3D animation through CSS 3D transforms, and 3D rendering through WebGL. Check out Google Chrome Experiments for some intense HTML5 demos using WebGL and other HTML5 technologies.
http://www.chromeexperiments.com/
There are also some great demos on HTML5's capabilities by Mr. Doob.
http://mrdoob.com/
Even Adobe acknowledges that HTML5 is the future. They have invested a lot of resources in creating HTML5 manipulation tools, and modifying existing software like DreamWeaver to support HTML5. Take a look at Adobe's new "Edge" software.
http://labs.adobe.com/technologies/edge/
In terms of portability, Google Chrome, Safari, Firefox, Opera, and IE9+ have good support for HTML5. It is also already built into Android, Blackberry, iPad, iPhone, and Windows Phone devices. HTML5 will also have a prominent role in application development on the Windows 8 platform.
http://ie.microsoft.com/testdrive/Graphics/hands-on-css3/