EasyChair
EasyChair is a free web-based conference management software system used, among other tasks, to organise paper submission and review. EasyChair is widely used in the scientific community, with reportedly more than one million users in 2014.
EasyChair has been in continuous development since 2002. As of 2015, the code base consist of nearly 300000 lines of code, and it has been used by more than 41000 conferences.