The Transcribe Bentham is an interesting crowdsourcing project in the humanities that has built an environment to involve people in the transcription of some 60,000 papers of Jeremy Bentham. The project is supported by University College London’s Centre for Digital Humanities.
I’m impressed by how they have adapted tools to develop the participatory environment rather than developing from scratch. The transcription environment is MediaWiki which has been adapted so that you can manipulate a manuscript using Zoomify. They have changed the WYSIWYG editor so that the toolbar available while transcribing corresponds to the tagging they want users to use. Using a wiki gives them the basics of user accounts, versioning, and editing. They also use WordPress for the site about the project and they have added discussion forums to the MediaWiki. There is a nice feature Random Page that takes you directly to a random page in need of editing.