Online mind mapping software MindV supports float topic. A float topic means a topic has no parent topic, and it can float anywhere on a mind map.
When you add a float topic, you can click the "Float topic" menu item,
The mouse cursor will change from arrow to a special icon.
You can move your mouse, find a place to set the float topic's position, then click there, a float topic will be added.
After that , when you want to move the float topic , you will find it is very hard to set the float topic position, because a moving float topic can be easily caught by other topics. This will happen when a float topic enter the red rectangle around main topic and it's subtopics.
And the tips is when you want to set a float topic's new position, you should collapse the whole map, then there are only main topic and it's first level topics visible, so you can easily move the float topic
Download MindV help files from download.com:
http://www.mindv2.com/ (Simplified chinese)
http://tw.mindv.com/ (Traditional chinese)
http://mindv2.cloudapp.net/ (Start mindv as guest user )
http://hi.baidu.com/mindvsales/blog (Hanson's simplified chinese blogs)
http://cn.linkedin.com/pub/hanson-chen/28/464/89a (Hanson's linkedin home page)