In the past decade, modern GPUs have provided increasing programmability with vertex, geometry and fragment shaders. However, many classical problems have not been efficiently solved using the current graphics pipeline where some stages are still fixed functions on chip. In particular, multi-fragment effects, especially order-independent transparency, require programmability of the blending stage, that makes it difficult to be solved in a single geometry pass. In this paper we present FreePipe, a system for programmable parallel rendering that can run entirely on current graphics hardware and has performance comparable with the traditional graphics pipeline. Within this framework, two schemes for the efficient rendering of multi-fragment effects in a single geometry pass have been developed by exploiting CUDA atomic operations. Both schemes have achieved significant speedups compared to the state-of-the-art methods that are based on traditional graphics pipelines. Copyright © 2010 by the Association for Computing Machinery, Inc.