FingerFiddle

I completely agree with Jace-BeOS, the quality of this program is hard to believe.

The sound is as dynamic as the one of the original instrument. The way it reacts to changing the stroke direction is very realistic, there's no way to do this with samples. The specific quality of each of the four string instruments is preserved very well: four players with four iPads (and four amplifiers) could do a very good impersonation of a string quartet.

At the same time the interface is easier to play than the original, and it's very configurable too: the pitch note is correct wherever your fingers land (as if having frets like on a guitar), but you can disable this feature if you want even more realism.

Another very welcome setting changes the pitch of each string. I set the intervals between strings to fourths instead of the original fifths, so that the fingering is closer to that of a guitar or bass.

Something very hard to do on the original: you can play three or four strings at the same time, not just one or two. :-).

As good as this program is, you can only play it via the touchscreen: it has no MIDI input. Driving it from my LinnStrument would be awesome. Matthias, what do you say? :-).