Nvidia Graphics Card that supports CUDA 7.5 with the latest drivers. You can find the download links for Windows here and the MAC download links for here

Info: GeForce GTX cards are fast and cost effective, but have less VRAM than Quadro and Tesla cards. OctaneRender scales perfectly in multi GPU configuration and can use different types of Nvidia cards at once. The only  drawback is that the Octane Render only use the lowest Vram if you have multiple GPU cards without the identical VRAM. For example if you have GTX 1080 with 8GB and GTX 1070 with 6GB, Octane will use the lowest Vram (In this case GTX 1070 with 6 GB). This is not a bug or fault, this is the design nature of "Parallel Computation"  

Internet Access