My friend the guitarist has an app on her cell phone which serves as a tuner. It doesn't just produce a pitch to be matched by ear, it 'listens' to the string and tell her when it's in tune, the same way a tuner does.

When we play music, there can be as many as 120 strings in the room. One folk harp, one double-strung folk harp, and a guitar. We don't have time for any kind of tuning except with fast and accurate electronic tuners.