JISC has released A Technical Review of Open Access Repository Registries: OpenDOAR and ROAR, which was written in 7/1/2011 and deposited on 7/5/2012.
Here's an excerpt:
This document provides a technical review of the capabilities, benefits and drawbacks of two leading Open Access Repository Registries (OARRs)—OpenDOAR and ROAR. Both systems are considered qualitatively and quantitatively with a view to identifying those facets which provide value for a repository registry service.
| Institutional Repository and ETD Bibliography 2011 | Digital Scholarship |