Just the stock OSX screen sharing over a network is convenient for me.
There are also remote desktop apps. There's also the Reaper web browser control feature. All kinds of free options for basic stuff. Simple OSX screen sharing is simple and immediate.
My first live sound rig using Reaper in 2009 was a late 2008 Macbook Pro and the first iPad.
(And then a UC-33 MIDI controller over a WiRanger USB wi-fi hub.) About 3 weeks after the iPad was first released the lightbulb went off for me. "Wait... This isn't stupid. It's a remote control for a computer with a screen! And this leads to running live sound roaming with a magic wireless remote control!