National Science Digital Library
The United States' National Science Digital Library (NSDL) is an open-access online digital library and collaborative network of disciplinary and grade-level focused education providers. NSDL's mission is to provide quality digital learning collections to the science, technology, engineering, and mathematics (STEM) education community, both formal and informal, institutional and individual. NSDL's collections are refined by a network of STEM educational and disciplinary professionals. Their work is based on user data, disciplinary knowledge, and participation in the evolution of digital resources as major elements of effective STEM learning.
Resource types available via NSDL include instructional materials, activities, lesson plans, audio/video materials, images, web sites, simulations, visualizations, tools, and services. NSDL also provides annotation collection and paradata (usage data) collections: comments, ratings, or usage information attached to existing resources in the NSDL.