A project based at the University of Michigan and funded by a worldwide group of libraries.
As of 1 January 2015, three TCP collections are publicly available: Eighteenth Century Collection Online, Evans Early American Imprints, and Phase 1 of Early English Books Online.
List of current open access titles is at the bottom of the page. All are published under the Creative Commons Attribution-Non Commercial-No Derivatives 3.0 license.
"The SPO Scholarly Monograph Series is an interdisciplinary collection of original, open-access scholarly monographs and essays published by the Scholarly Publishing Office of the University of Michigan Library."