Self and peer assessment offers benefits for enhancing student learning. Peer moderation provides a convenient solution for awarding individual marks in group assignments. This paper provides a significant review of peer-mark moderation, and describes an award winning, web-based tool that was developed in the UK and is now spreading across the world as an open-source web application. It is available for use in any discipline. Qualitative research, at the home institution over several years, reinforces the evaluation of quantitative data extracted from the system and from an extensive user survey to confirm, update and strengthen the previous literature. The research also describes new insights into the thoughts of students, who appear to recognise the transparency that automated moderation offers. The statistics suggest few incidences of team-collusion when entering data, but indicate that peer-marking behaviour is influenced by group size, selection method and year of study. Students comment positively on the recognition of their levels of achievement within a team.