The PhET website at the University of Colorado in Boulder has a large collection of science simulations for teaching chemistry and physics, available in many languages. This page describes the Activities Database, which is searchable by topic, grade level, and language, and contains lesson plans, homework tasks, lab materials, and more. The activities are often accompanied by downloadable files in Word or PowerPoint. If an activity has a gold star, that indicates that the PhET team reviewed it and it met their standards, although not everything has been reviewed.