Questions about entering and leaving Nicaragua are common here. Unfortunately, the answers are spread all over the site because there is no one, easy, cookie-cutter answer. That is, it depends on what other country is involved, your citizenship, legal residency, direction and so much more.
One of the hardest parts is going to be not duplicating information. For example, there are going to be an assortment of fees which apply to various conditions. My idea right now is to put all the fees on one page which you can reference once you follow down through the pages to collect the information on your particular situation.
This set of pages in intended to be the authoritative answers. If you see an error, add a comment. We will incorporate the comments into page updates from time to time. If you want to discuss the various issues, there is a whole set of forums about immigration at http://www.nicaliving.com/forum/15