Please curate, according to the needs of your students.
An accessible, visually appealing site: http://theoatmeal.com/tag/grammar.
A useful site for writing process, rhetorical modes, and basic grammar (including short videos): http://www.oercommons.org/courses/english-composition-1/view
A good site for writing process and rhetorical modes: https://courses.lumenlearning.com/suny-englishcomp2kscopexmaster/
A particularly good site for plagiarism: https://www.indiana.edu/~academy/firstPrinciples/index.html
A great site in general: https://owl.english.purdue.edu/owl/