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Re:Facebook’s F8 Agenda: Deep linking for mobile apps by alaskamiller on Sunday March 09, 2014 @01:01AM (#7367644)
From 2004:

<a href="aim:GoIm?screenname=myscreenname&message=hello">x</a>

Re:Facebook’s F8 Agenda: Deep linking for mobile apps by robmil on Sunday March 09, 2014 @07:32AM (#7368174)
mailto: is the same principle and has been around since the 90s.