We examine student peer review, with an emphasis on formative practice and collaborative learning, rather than peer grading. Opportunities to engage students in such formative peer assessment are growing, as a range of online tools become available to manage and simplify the process of administering student peer review. We consider whether pedagogical requirements for student peer review are likely to be discipline-specific, taking computer science and software engineering as an example. We then summarise what attributes are important for a modern generic peer review tool, and classify tools according to four prevalent emphases, using currently available, mature tools to illustrate each. We conclude by identifying some gaps in current understanding of formative peer review, and discuss how online tools for student peer review can help create opportunities to answer some of these questions. (Contains 2 tables.)