I was thinking that Steam is the go-to multi-platform game selling/publishing service, and that every major platform has it's own software publishing store (e.g. Mac App Store, Ubuntu Software Center). Yet, is there a multi-platform service similar to Steam that allows you to publish software?
Well, Steam sells software now. Not exactly the answer you were looking for, but they began selling regular software packages awhile back.<p>I don't know how multi-platform their software offerings are, though.