The ARB_compute_shader extension allows arbitrary workloads to be done on the GPU. Compute shaders in OpenGL are somewhat similar to OpenCL but there's many low-level differences, among them is that compute shaders are still written in GLSL. The extension is documented at Khronos.org.
As of today the ARB_compute_shader is starting to hit mainline Mesa. Besides the usual caveat that this work is just for core Mesa plus Intel's hardware driver, the ARB_compute_shader support is also hidden for now behind an environment variable. INTEL_COMPUTE_SHADER=1 must be set for utilizing the GLSL compute shaders with the Intel Mesa driver at this time. This work hit today and will be officially christened with the Mesa 10.2/11.0 release.