This does seem a bit of a limitation. It's 2017 not 1999.
I'm not directly comparing Outsystems with any of the following but: Ionic, Phonegap, Appcelerator, FuseTools, NativeScript, Appery, Screendy, Appgyver... in fact ever mobile dev platform that comes to mind has multi-platform tools either in the native GUI, command line or through a browser. Appery & Screendy have really rich visual IDEs for building apps & wiring up components to REST backends etc. all done in the browser.
Even Microsoft's Xamarin Studio has a Mac version! Yet the OutSystems offering is tied to Windows....so that people can develop apps which run on... Android and iOS?
It's a real shame.
Steve