Teammates is a system where peers can rate and give feedback about other group members. The instructor can fully customize for what the needs are of the course. If you want others to see their feedback. If you want them to see their score based on their groupmates. It can also allow you to download the data and you can see how well each group worked and what you can improve upon next time.  

This world renowned tool used by many colleges and universities has many LMS tie ins and allows peer to share and review each other's work and provide the necessary feedback to improve their projects. It also has many in course work tie ins to improve online collaboration with discussions and replies to course related topics. 

This piece allows teachers to create assignments, after students have worked on it completed and submitted it. It goes to a peer for feedback, and then the person can go back make changes before the teacher reviews. This allows for online collaboration and allows for students to feel more of a sense of community. If they know a peer will be reviewing their work it may make them feel that they should put in a better effort if classmates are going to see it.