Opera and Google Earth are good examples of such apps - they suck. Both have non native and ugly user interface. So if you your app does more or less what other apps do, but looks like this, people will prefer the native cocoa apps.
AppleScript is nice tool for special jobs, but you do not like to write complete apps with it. It is too annoying to write, slow and hard to debug. Use it to script other apps.
If you want to create Mac OS X apps, forget about multi platform stuff - your customers do not care if your app runs on other platforms, and they will ignore your app if it does look and behave like a great Mac app.
This is true also for their desktop apps user interface. This trend started with Mac OS 9, when QuickTime started to use that stupid brushed metal theme. Currently there few themes in Apple apps; Aqua (Mail), brushed metal (Safari), iApps (iTunes) and pro (Final Cut).
This make it tricky for 3rd party apps - you have to ask yourself which group your app belongs to. If you want to create iApp or Pro interface, you have to simulate the design because there are no ready made interface elements using those styles.
The same list entry can be moved between several lists using the same type.
If the struct need to be in multiple lists in the same time you can keep multiple list entries in the same struct: https://github.com/freebsd/freebsd-src/blob/69413598d2660054...