TheOpenPresenter

Getting something onto a big screen still means cable roulette, adapter hunting, and a laptop stranded at the front of the room. TheOpenPresenter fixes that: the screen loads a URL, and you drive it from your phone, tablet or laptop. Nothing to install on the presenting machine, and no mirroring your whole desktop. Everything syncs in real time, so someone else can fix a slide while you're mid-presentation. Fully open source (AGPL-3.0). Self-host it for free, or use the hosted version.