Broadcast 2000 and Cinelerra from Adam Williams was the first universally available application that enabled you to edit and layer multiple images and watch them in real-time with minimal or no rendering, whatsoever. In fact, Cinelerra was first 64-Bit editing system, released in the Spring of 2003 and first demonstrated at SIGGRAPH in the summer of 2003 in San Diego.
The processing power of Cinelerra enables you, on a properly configured system, to see multiple layers render in real time in your program window. In fact, Cinelera does not limit you in the number of layers that you decide upon in your edit. So, when you set a dissolve or cut or any number of effects in Cinelerra, when the system is configured correctly, you can see the edit happen immediately. This is done through the software as designed by Adam Williams, the power of the Linux kernel with needed improvements as designed by the developer, the capabilities of the 64-Bit system, and the integration of the processor in the GPU.