While there was the Libre RISC-V GPU effort aiming to provide an open-source GPU accelerator based on RISC-V, it ultimately turned into Libre-SOC with a focus now on the POWER ISA. Meanwhile Vortex is continuing to mature as an open-source, FPGA-based RISC-V GPGPU processor.
Vortex is a RISC-V GPGPU currently for FPGA-based implementation with either the Intel Arria 10 or Intel Stratix 10 working. This general purpose GPU makes use of the RISV-V RV32IMF 32-bit ISA and can yield up to 1024 threads at 250MHz.
Vortex provides support for OpenCL 1.2, but obviously with being an FPGA-based implementation and an early design, it’s only capable of roughly 128 Gflops for the compute bandwidth. The memory bandwidth is rated for 16GB/s.