I have a view with lists of 10 nodes with a node display type (not rows). Every node has a flag. How to make possible to flag ONLY one node of these 10 nodes, for example if you have flagged one node - you cannot flag another one untill you unflag flagged one. Just like a best answer functionality on this site. Thanks :)
Is Flag Limit module what you are looking for?
This module allows any flag (for example: bookmarks) to have a limited number of items.
There is a new feature in the 7.x-1.x branch that optionally lets you limit the number of flaggings each item can have. Once the limit is reached, nobody else can flag the item.