Reopening a window closed accidently!
I often work fast, especially with keyboard shortcuts so it happens often that I accidently close a window of the web browser. It is of course possible to simply reopen it from the History. Unfortunately, the one that I closed is not always at the top of the history. It might be a page that I loaded an hour ago. There is a very cool feature in Safari that reopens the last closed window. If the last closed window had several tabs, it will reopen all the tabs (although it is unlikely to close a window with many tabs because Safari warns you first). There is no keyboard shortcut assigned but you can create one in System Preferences (check previous tips). The feature is located in the "History" menu of Safari and is called "Reopen Last Closed Window".