Ask HN: Who is giving(course/book etc.) free now?

Pluralsight is fully free for this one month https://www.pluralsight.com/offer/2020/free-april-month

Currently Unity is giving all the courses free. https://learn.unity.com/

Book Linear Algebra Done Right - Book is free until the end of July. https://link.springer.com/book/10.1007/978-3-319-11080-6

Who else is giving free content in this lock down period?