Try the ukulele.

I never really got away with guitar, but I have recently picked up the ukulele and am making progress and having fun.

As suggested above, Baritone uke is tuned like the top four strings of a guitar so guitarists should find it an easy transition. Alternatively go the whole way and go for one of the smaller ukuleles with the standard re-entrant tuning which gives them something of their character. Soprano, Concert and Tenor ukuleles are all tuned the same: GCEA but the G is tuned an octave higher - just a tone below the A string. I have small hands and have a concert uke and find it comfortable to play and it has its own character which is different from the guitar. I started with the a cheap soprano uke, but have upgraded to a better quality concert uke which I find more comfortable to play. Some suggest Tenor uke makes a good starter for a guitarist as the size is closer to what you are used to.