www.pearsoned.ca/highered/peerscholar/ is a web service in which you can have students submit work, set up peer evaluation groups where anonymity protects identity, and the teacher sets up a rubric.
The students evaluate a few of their classmates' work and give feedback using the rubric as a guide. In addition, the teacher can put in an exemplar so that the students can see what is expected vs. what they have done themselves. The exemplar can be added as if it were a student's work, which often raises the bar, or leads to excellent dialogue about ways to achieve the gaps in the rubric.
This is not a free site, and I'm looking for something similar that's free or affordable and doesn't require an institutional license.