Apostrophe is an open source CMS designed for maximum flexibility with a minimal learning curve.
You can check out a live demo here.
This site provides developer documentation for Apostrophe 2, our next-generation version version built from the ground up with node.js. You can find information about the older PHP-based version here.
The Apostrophe project is led by P'unk Avenue, a design and build firm with a special focus on positive social impact, urbanism, health & wellness, arts & culture, and education. Giving back to the open source community is part of that focus.