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As far as I can tell it's 7 so far. Nine more potential operating systems and three through emulation. Oh, and AmigaOS (or even AmigaDE) is not in an early stage of being ported to Pegasos, unless you count people shouting "we want it" as an early stage.
If I were to be extremely kind I'd say 9 total so far, since the MOL system runs so well it's almost as good as native. However, AmigaOS 3.x is going to be with emulated CPU and thus quite a bit slower. At least till Bernie works his magic.