 <p>I am the product manager for the OpenPlug tools.</p> <p>Our tools are not the only ones that allow IPA signing on Windows (you mentioned marmalade, but there is also Adobe CS5/AIR/Flash Builder, and certainly others ...)</p> <p>As far as I know, Apple hasn't banned any app built with those tools on the ground that they were developed on a non-Apple-branded computer.</p> <p>For publishing your app you anyway need to access iTunes Connect from a Mac.</p> <p>Having the possibility to sign IPAs on Windows facilitates the dev/debug cycle on device if you are a developer with a Windows host.</p> <p>Technically, the signing tools are available open source from the Mach open source distribution of MacOSX. You can refer to the comments section of this post on Corona's blog (another app development tool) for discussion about legalities: <a href="http://blog.anscamobile.com/2010/03/does-flash-cs5-for-windows-violate-the-iphone-developer-agreement/" rel="nofollow">http://blog.anscamobile.com/2010/03/does-flash-cs5-for-windows-violate-the-iphone-developer-agreement/</a>.</p> <p>The last time I looked at Apple's agreements, its only the "SDK" (i.e. xCode and associated iOS SDK) that was only allowed for use on Apple-branded computers only.</p> <p>Hope this helps</p> <p>Guilhem</p>