Dear Dr Hamid Mohsenzadeh , Turnitin is most widely used. Beside of Turnitin, you may follow other online plagiarism checker, but frankly telling I do not trust those online links when it comes to confidentiality of the materials. So, please think before you submit your materials to online platforms.
There is none! I use Turnitin but the decision of whether the text is plagiarised remains to be made by human beings (rather than a softwae programme)!
Actually, plagiarism is an area to which the adage of "prevention is better than cure" applies best! Teaching your students how to cite and quote properly and paraphrase the other authors' words / ideas so that they can write without resorting to plagiarism is the best and accurate way of minimising plagiarism!