iSLCollective


Internet Second Language Collective is a community of language teachers from around the globe who share their home-made worksheets on this free-to-use platform! Currently, you can find here Word doc/docx and ppt/pptx (power point) files. It's for all language teachers, whether teaching in schools or doing one-on-one private tutoring. The site has 6 platforms for the teaching of English, German, French, Spanish, Portuguese and Russian. You can download all ESL teaching materials free of charge. 
https://en.islcollective.com

Quizlet


Quizlet team wants to help students and their teachers practice and master whatever they're learning. Quizlet provides engaging and customisable activities thanks to contributions from people everywhere. Anyone can use Quizlet to study and learn content created by other users, or to create your own custom study sets. You can also share sets with friends, classmates or your students. 
https://quizlet.com

Khan Academy


No ads, no subscriptions. Khan Academy is a not‑for‑profit organisation. They believe in a free, world-class education for anyone, anywhere. They rely on community of thousands of volunteers and donors. They offer practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. They tackle math, science, computer programming, history, art history, economics, and more. Their math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. 
https://www.khanacademy.org