Xylo
Paranormal Adept
The latter is the only theoretical alternative I ever heard of. If anything else could be a basis of life, in the real world, biochemists probably would've thought of it by now.
Even on earth we have other than carbon based life...
http://ijs.sgmjournals.org/cgi/content/full/55/3/1069
Sure we didn't discover it until very recently, but it's there and it's not theoretical.