In June I wrote about the VOA's free, online English courses and materials, appropriate for adult ESL learners on several levels. It's at https://learningenglish.voanews.com.
Now I've discovered free online beginner and intermediate ESL courses offered by the Sacramento County Office of Education. They also offer a course to help prepare for citizenship. Students can study on their own or with the help of a teacher. In addition they offer a "Skills for the Nursing Assistant" course. Learn more at their their "USA Learns" site at https://www.usalearns.org.
In addition, check out the MOOCs offered by the US Dept. of State Bureau of Educational and Cultural Affairs. (MOOC stands for Massive Open Online Course.) I haven't studied these in depth, but they appear to be aimed at advanced learners and perhaps students on an upper-intermediate level. See their variety of current and upcoming offerings at https://www.openenglishprograms.org/MOOC.