This is open-source project: https://github.com/intellicommand/intellicommand
IntelliCommand - an extension for Visual Studio 2010/2012/2013 which helps to find the short keys. It shows the help windows with all possible combinations when you press Ctrl or Shift or Alt or their combinations (hold it for about 2 seconds to see this window). Also it shows the list of possible combination when you press first combination of chord shortcut keys, like Ctrl+K, Ctrl+C (this combination comments selected text in editor).
Intelli Command shows all available shortcut keys for combination of Control + Shift after couple seconds:
Ctrl+K was pressed. Visual Studio waits for second combination:
Available options for Intelli Command. The delay of showing Intelli Command window. Customization of Intelli Command window look: