Parlo provides instruction in English, as well as other languages. It's approach is called Virtual Immersion - integrated language instruction and exploration of international cultures. The site includes an excellent selection of materials for students as well as teachers. This online course teaches English as it is used in the United States. The exercises include some excellent word jumbles with feedback.
Teachers can also build their own online tests at the site.
Well worth a visit. The Tower of English is a fun place for ESL students to use and practice English. You'll find lots of interesting activities and projects here. Just jump into the elevator to get around The Tower. Used under License.