Open Education STEAM Curriculum Development Resources - license free

These resources, to the best of my knowledge, provide some form of an open license.

Image Web Sites 

1. Pexels | Open Clip Art | Pixabay | Unsplash 

Science

Interactives and Simulations

1. PhET | The Concord Consortium

1. Textbooks

1. OpenStax (all textbooks)
1. Anatomy and Physiology | Astronomy | Biology | Chemistry | Physics
2. CK-12
1. Earth Science For High School | Earth Science for Middle School

Math

1. Textbooks

1. OpenStax

[https://www.pexels.com/search/Buffalo/]