Memofon is a text driven mind mapping / to-do list app which runs in your browser. Putting together a new map is simple, using indents to indicate sub-levels and links. It also has a basic wiki-like syntax.
As a test I put together a mind-map of out Mince Pies & Murder adventure showing a timeline, locations and characters.
It works quite well be the interface isn't perfect. Expanding and contracting nodes isn't intuitive. Rather than clicking on the node to expand/contract you click on a little + or – symbol. You must also contract one node before opening another rather than this happening automatically when you try to expand a node.
For adventure mapping, the big limit is the nesting structure. If one location is linked to multiple places (such as the Back Stairs in Mince Pies), there is no way to do this other than duplicating nodes.
All in all, it is a good app and one I will be experimenting with further.