Mesa might be an option for you.
From their website:
Mesa is the OpenGL implementation for several types of hardware made by Intel, AMD and NVIDIA, plus the VMware virtual GPU. There's also several software-based renderers: swrast (the legacy Mesa rasterizer), softpipe (a gallium reference driver) and llvmpipe (LLVM/JIT-based high-speed rasterizer).
When using Mesa you can set the LIBGL_ALWAYS_SOFTWARE
environment variable, which will cause Mesa to "always use software rendering".