In Flash Player 10, Adobe added some semblance of 3D functionality. While it was now possible to move, rotate, and scale Flash objects in three dimensions, you could still only work with 2D objects, as those were all Flash could draw. It wasn't true 3D, but what is usually referred to as 2.5D. Now Adobe is ready to take the next step with Flash, which is to bring true 3D support in Flash 11.
3D engines for Flash had already existed since before Flash Player 10 came out, however with Flash Player 10 such engines were further empowered. With the new 3D APIs, codenamed "Molehill", which will come in the next major Flash Player release, Flash is about to become an even more attractive platform for online gaming.
A future version of Flash will expose low-level APIs that will allow developers to create rich immersive 3d interfaces or games which are rendered using the GPU as far as possible. In case GPU acceleration is not possible the content will still be viewable, albeit with lower performance, using the CPU.
Since these APIs are rather low level, most people will be more comfortable using 3D engines such as Away3D, Papervision, Alternativa3D etc to access them instead of using the APIs themselves. Best of all such engines can be developed to use the new low-level APIs while keeping their own API the same, allowing developers to take advantage of great boosts in performance without changing much of their code.
The advantages for RIA developers are obvious, "Molehill" gives them an additional dimension to play with, allowing for richer 3D product demos, more immersive interfaces and better quality games. Best of all these 3D features will be available on mobile as well as desktop, enabling truly portable 3D content. In 3D features in Flash Player, Adobe will also release a 3D enhanced version of Pixel Bender.
Flash isn't the only one adding 3D features though. 3D rendering direct in the browser is part of the WebGL specification, and will allow 3D content to be rendered directly in the browser. It is still in development, and is not yet available in released browsers. Even with more support in 2011, it will still take much more time before 3D support in browsers reaches acceptable penetration. Till then Flash Player seems like the best cross-platform solution for 3D on the Web.