The mesa software renderer (both the "old" pre-gallium swrast and the "new" gallium softpipe/llvmpipe), do support most of GL3.2. The only major thing missing is support for multisampling, hence they are not advertising full 3.0 support.
Update 2017
Current versions of mesa's various software rasterizers now do claim to support up to GL 3.3 in a core profile. (The progress can be tracked on https://mesamatrix.net/). However, there is a caveat, as documented in mesa's feature.txt:
freedreno, llvmpipe, softpipe, and swr have fake Multisample anti-aliasing support
which means they still do not fullfill the requirements of the GL 3.0 spec. However, in most cases, this will not matter in practice. But one should still be aware of that limitiation.