ironman - The opposite of exclusive is according to the english dictionary;
divided, part, partial, shared, unlimited, unrestricted, multiple.
And what is a platform? The english dictionary defines it as, in this case, a platform that allows playback of software.
So if a software is able to be played on multiple (not exclusive) platforms (something that plays software). The word for it would be what? Even if its a OS software platform (NXE and WIN7 - two different platforms), the word would be Multiplatform.