Wasn't there OmniGraffle on the Mac even before Sketch? Seemed to me in the beginning that Sketch was an exact clone of OmniGraffle with a little nicer interface. Sketch evolved a lot from that point on.

Edit: OmniGraffle 1.0 launched 2001 [1], Sketch started 2008

[1] https://www.macworld.com/article/1002530/omnigraffe.html