One certificate will sign on ALL supported platforms. Microsoft Authenticode (DLL, EXE, COM, etc), Java, Mozilla, Android, Adobe AIR, Flash, Silverlight, MS-Office and OSX/iOS.

** PLEASE NOTE that Apple (not anyone else) introduced a feature in to their Gatekeeper software that will cause OSX to *only* recognize Apple-issued certificates for software. This feature is, amazingly, turned ON by default. So while Comodo certs are still recognized on Apple's OSX, users with that setting turned on may see signatures come up as Unknown. This DOES NOT affect Java apps or applets running on OSX, only native OSX software.