From PubPub, the MIT open source platform:

The community is still working on the processes, workflows, standards, and values that will support this emergent form of publishing. But that shouldn’t stop anyone who wants to explore these models from starting now. With PubPub, anyone can publish and distribute meaningful, impactful reviews with appropriate metadata that can be picked up by aggregators in about an hour — at no cost and with no technical expertise required.

The post is a detailed guide to how the platform—which we use for—can be used as a review layer on top of other preprints services, a la PREReview and eLife’s Sciety.