http://iscoresports.com/

How would you score batter gets a hit and advances to second on an unsuccessful attempt to throw out another runner at third? Double or single with advance to second on the throw?
Thanks.

Go to game settings and set Scorekeeper Level to Advanced and you will be asked about the original batter at the end of play entry. See the following link in the iScore documentation:

http://iscoreleagues.com/manual/#h.2q4k99qxrzsl

Thanks. Are there any circumstances where the above play would be scored a double for the batter?

If you as the scorekeeper feel the batter would have been safe at second even without the throw to third (i.e. if nobody was on and the batter would have made a double), then you would score it as a double. Otherwise it would be single + advance on throw.