MSN Messenger was Microsoft's popular instant messaging service in the late 1990s and 2000s, and its contact online alert became one of the most recognisable sounds of that era. The chime played whenever someone on a user's contact list signed in, turning an ordinary login into a small social event. As MSN declined and closed in favour of Skype, the sound survived through YouTube compilations, nostalgia videos and social media clips, where it now signals retro internet culture and the excitement of a friend coming online.