After reading the Mac App Store guidelines it's still unclear to me whether apps developed using Macruby or apps using the Cocoa WebView object as the sole UI surface are allowed.

I would like to know if it is allowed since it might speed up the development of some apps that have modest UI and OS integration requirements.

Clause 6.3 ("Apps that do not use system provided items, such as buttons and icons, correctly and as described in the Apple Macintosh Human Interface Guidelines will be rejected.") comes closest to not allowing a webapp-wrapped-in-webview, although "do not use [...] correctly" is a vague statement.

I found the Mac App Store requirements in this pastie: http://pastie.org/1236378 via this article (The Register): http://www.theregister.co.uk/2010/11/01/mac_app_store/