Hi,
Actually the next Major version of BeerSmith is being written using wxWidgets which is cross platform. I already have it running (though its still an embryonic version) on my Mac and Windows PC. I have a Linux system ready as well, but need to move it over. However the Mac and Linux are similar in many ways (both gcc, both unix based, etc), so I don't think the leap from one to the other will be large.
However there is still much development to be done on all the versions - so be patient. No release date yet, but I intend to have the PC and Mac versions released close to each other with the Linux to follow behind that.
Cheers,
Brad