AjaxBatchUndelete is based on a script written by Splarka on Wikipedia and rewritten to use jQuery by Grunny. It provides a link to a batch undelete form that allows you to list pages to be undeleted, through the API. This script is, essentially, the opposite to AjaxBatchDelete and functions similarly. Nerfmaster8 and Noreplyz have updated the script using the second version of AjaxBatchDelete.
The option to use the Batch Undelete script will appear under your "My Tools" menu. In order to undelete a batch of pages, just add the page names (not page URLs) in the form, each on a new line, and proceed to undelete them with a set reason. The script will stop when it reaches an empty line, and it can be terminated early by blanking the list of pages remaining to be undeleted.