NetBeans Key Promoter
When you click a menu item or toolbar button, NetBeans will advise you about the matching keyboard shortcut, if a matching keyboard shortcut exists. The advice is displayed in a green display area in the status bar.
Related documentation: https://blogs.oracle.com/geertjan/entry/key_promoter_plugin_for_netbeans
Screenshot showing green display area in the status bar, with "ctrl-s", the keyboard shortcut of the most recently used action:
