I think Quicksilver is the one that started the trend that has persisted for the last 16 years or so — and that trend certainly increased with Spotlight’s intro

I think Quicksilver is the one that started the trend that has persisted for the last 16 years or so — and that trend certainly increased with Spotlight’s introduction with Mac OS X 10.4 Tiger in 2005 — although as mentioned below, LaunchBar predates it by 6 or 7 years. But Quicksilver really introduced (as far as I remember) the UI that most other modern launchers still use, and that Spotlight later “stole” — which is to do the search in the middle of the desktop. LaunchBar is probably the OG, but I think most of what has come since (including LB, which remains excellent), was influenced by Quicksilver in the early aughts.