Plag Tracker is a service that students can use to check their essays for possible plagiarism. To use the service students simply copy and paste text into Plag Tracker. Plag Tracker then scans it to find sentences and phrases that appear in other works on the web. If Plag Tracker detects a possible incidence of plagiarism, the link or links to the source is listed for students.
Plag Tracker does offer a "premium" service in addition to the free plan. The premium plan allows users to upload documents instead of copying and pasting text. The premium plan also promises faster scan times, but I didn't shell out the $15 to test that claim.
Applications for Education
The free version of Plag Tracker could be a good tool for students to use before they turn in a research report. Have students run their essays through it to make sure they haven't accidentally plagiarized or improperly paraphrased information they used in writing a report.
Click here for eight other resources for preventing and detecting plagiarism.