I actually liked the linked article about the art of OKR more. While I've been exposed to SMART goals (Specific, Measurable, Actionable, Realistic, Timeframe?) as a missionary, for some reason it didn't ever really carry over into the real world.

I do feel like OKR has a fair amount in common with GTD as well, though I'm not actually familiar enough with GTD to assert that, though from the outside they are similar.