Headspace
Headspace is a 3D mind-mapping / outlining tool. It lets you construct heirarchical lists in a 3-D space and link between them. Use it to construct lists of ideas, game information, random thoughts, etc.
It’s available on Apple iTunes App Store for $2.99. Here is the link:
If you just want to ‘test-drive’ Headspace, there’s a free version! It only allows you to keep one ‘space’:



