If the user's browser or machine crashes while editing a node; the edits will be presented to the user the next time they return to the node. The user may toggle back and forth between the last saved version and the version with the edits that were lost and select which of these they would like to continue with.
The admin can configure how often is the form saved and which content type benefit from this feature.
Unpack in your modules folder (usually /sites/all/modules/) and enable under Administer > Site Building > Modules.
· Drupal 5.x/6.x
· Drupal jQuery Update module
· jQuery Form plugin