There is some software called Yousician that gives you songs/tunes to play and it critiques how well you do. It starts off with really simple tunes and progressively gets more difficult.

I've used Yousician for the piano and liked it. It's also compatible with the Ukulele and, as you're asking, the guitar. I found it missed some of my ukulele playing, but it could just have been me playing poorly.