More sites like 1text.com and Quilbot.com can also be used to check for plagiarism, and they are free for certain stages but require an upgrade when requesting premium service.

Do we actually need all these?
A good piece of content generated from one's own thinking should have nothing to do with plagiarism, unless you copy some part and think it may not show up on the websites you are checking. Meanwhile,  there are other plagiarism checkers that are perfect and can expose such minor plagiarisms.