I've run Linux in the simulator they supply with the lowrisc project. Not a big thrill, but the platform has promise. It's way too early for the devs to be wondering about memory maps and frame buffers, but it's definitely a platform to keep in mind as time progresses.
Right now you can run a RiscV machine in FPGA on a Parallella board, and there is an Arduino compatible RiscV MCU board (done in hard silicon) available for sale. That board is the SiFive one mentioned by someone already. They say they're working on bigger scale stuff though. They have a dev board available with a bigger FPGA, that runs a RiscV machine and Linux OS variant. We'll be watching them to see how it goes. The sites for info on the instruction set are at riscvfoundation.org and riscv.org.
Been thinking about getting one of the little MCU boards just to plunk around with it.