New Textbook options

[eriehomeschooler]

A company in the town where I'm from is launching a new series of online textbooks that are free. The first one is a math textbook and it looks pretty good so far. The whole book isn't online yet, only parts of it, and I don't know when the final book will be up, but I'm going to try to incorporate it into my teaching.
Here is a link: math.andyou.com
There are a lot of free textbook resources like this popping up. Another one I found is called Bookboon, but it is a European company, so some of the text books are harder to follow, but still useful.
Anyone else know of any good free textbook options for home schoolers to use?