How to display the current mapping for keyboard shortcuts in realtime?

This program shows all keyboard shortcuts that use the ⌘ (command) key, just by pressing and holding command. http://www.cheatsheetapp.com/CheatSheet/

It does not show shortcuts that do not include command, but is quick and easy to use.

I use KeyCue. It's similar to @avv's recommendation but more customisable.

Woohoo! After some more looking, I've found https://pqrs.org/osx/karabiner/ which does everything I want! Please let me know if there's a lighter-weight alternative…

To see keyboard events using Karabiner:

• open the app
• enable Karabiner under System Prefs > Accessibility
• (maybe restart the AX notifier)
• click the icon in the menu bar (near the time)
• select Launch EventViewer

The event viewer will show a log of events like:

eventType:FlagsChanged    code:0x37       name:Command_L       flags:Cmd                                misc:KeyCode::COMMAND_L  characters:    
eventType:FlagsChanged    code:0x37       name:Command_L       flags:                                   misc:KeyCode::COMMAND_L  characters:    
eventType:SysKeyDown      code:0x1        name:                flags:                                   misc:ConsumerKeyCode::VOLUME_DOWN
eventType:SysKeyUp        code:0x1        name:                flags:                                   misc:ConsumerKeyCode::VOLUME_DOWN
eventType:SysKeyDown      code:0x0        name:                flags:                                   misc:ConsumerKeyCode::VOLUME_UP
eventType:SysKeyUp        code:0x0        name:                flags:                                   misc:ConsumerKeyCode::VOLUME_UP

(scroll right to see the flags)

It may be useful to click the Preferences tab in EventViewer to 'always show on top' and uncheck 'hide ignorable events'.