The client has been released under the GPL. Because of this, Quake II runs on Linux under any architecture. I've seen reports it works on SGI IRIX (MIPS). So it is portable (any game brought out for the N64, DC or PS is portable). You can basically run it under about any OS :) there's no need for WINE or CrossOver.
Please take note the artwork is still proprietary however with a demo and loads of 3rd party map you might not need it.
PS: besides bronze/silver/gold/unsupported/not tested/honorable mention i suggest another ranking: "native supported" or "open-sourced".