Turnitin

An Internet-based, US-American plagiarism-prevention service, which was established in 1997. High-schools and universities have to buy a license to use it. It allows them to "turn in" essays of their students. The software then checks if the document contains unoriginal - plagiarised - content and tells the teacher.
If the appropriate settings are used, learners can upload their work ahead of the deadline and generate a similarity report to help them to make improvements to their paraphrasing of others' work.