I've recently heard that plagiarism checker Unichek has integrated with Google Classroom. You can find detailed information about it in this article: https://unicheck.com/blog/plagiarism-checker-google-classroom/
From myself, I can say that I've been using this tool for a year now. It helps me always to be sure my students have their own thoughts on some topic and are able to think critically, which I think is one of the most important skills nowadays. When I had heard this news about their integration with Google Classroom I was so happy. GC is my favorite LMS and after their integration with this checker, it's easier for me to check my student's assignments for plagiarism.
Also, i don't know whether any of other checkers are integrated with Google Classroom. I've heard only about this one.
Nancy, thanks a lot! I'll check it )
You're welcome, Deborah!
I know only Unicheck, it integrates with Google Classroom via API https://unicheck.com/education