Cerebro

You want an Alfred-style "hotkey summons a box, type to act" tool, but open and free. Cerebro is that: an open-source launcher that, once summoned, searches apps, looks things up, does math, and runs plugin actions.

Features

Quick Summon: A hotkey opens a search-and-act box.

Plugin Ecosystem: Extend search and actions with plugins.

Free & Open: Freely usable and extensible.