GOG Connect is back and it brings with it the chance to redeem Torchlight II if you have it on Steam.
I did ask about the status of getting the Linux build of the original Torchlight onto GOG, they replied, but they couldn't give me an answer on it. Still, a DRM free copy of Torchlight (if the Linux build eventually comes to GOG) & Torchlight II from GOG is a pretty sweet deal.
You've got two days left to redeem them according to the page.
On top of that, if you own either title from Runic Games purchases directly, you can input your key here, to redeem it on GOG too.
If you don't own Torchlight II, GOG currently have it on sale with 75% off so that's a pretty slick deal for Linux gamers.