Open Educational Resources Commons. They took off running with some of the things they found on the OER Commons. In fact, it was through one of them that I learned about Math Open Reference which was linked to a mathematics lesson on OER Commons.
OER Commons is a place for educators to post lessons and lesson materials that others can use. There are thousands of lessons organized by content area and grade level. After you've made your initial selections of content area and grade level you can refine your search by lesson type, material, media format, and usage rights.
Applications for Education
One of the great qualities about teachers is that, for the most part, we're very willing to share our ideas and lesson resources with each other. OER Commons is a great online example of that quality found in teachers. If you're a new teacher or you're teaching a new grade or subject this year, you're probably trying to develop a lot of new lessons this year. If you're looking for ideas and or materials for those lessons, give OER Commons a look.