Tired of Turnitin? Confused by Copyscape?
Plagium is, yes - another text matcher (otherwise mis-known as a plagiarism checker)! Have a look, though, it's very easy to use and produces its results as big red balls on a timeline: what's not to like about that?
They say: "Plagium is an innovative, fast, and easy-to-use means to check text against possible plagiarism or possible sources of origination. Simply enter text that you would like to analyze into the text box and let Plagium do the rest of the work.You can also check the contents of an entered URL for its sources."
I tried it out and quite liked its ease of use - might be useful if you have a suspicion and might wish to have a chat with a student about the implications of the matched text that you've found.