SmartMusic has a lot of great resources built into the program to assist with assessment and feedback; however, it is also limited in that it is a computer determining pitch and rhythmic accuracy. While this feedback is better than none, I caution educators who use this as the only form of assessment and feedback. I personally think there is more to music than pitch and rhythm and I think that technology should encourage students to think as musicians rather than simply telling students when they are and are not musical based on two criteria.
Noteflight allows you to write music online and embed the music as play along files on your website/blog. The service is free to use and does not require software to create the files (unlike Scorch and SmartMusic).