Does anybody here have knowledge or experience regarding crowdsourcing transcription services?

Some of my day-to-day work revolves around a thing affectionately called the Catholic Portal. [1] The Portal is an alliance of members who provide access to rare an infrequently held materials of a Catholic nature. Many of our member organizations are tiny, really tiny, and consequently they do not have very many fiscal resources. On the other hand, they are very rich is primary source materials. As these materials get digitized, there is a need/desire to transcribe them. (OCR will not be an option.) 

I was wondering, do any of you know of any services supporting the crowdsources of transcriptions, or maybe there is a piece of (open source) software allowing me to publicize things to transcribed, and then allowing somebody to actually do the work?

[1] Portal - http://catholicresearch.net

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Eric Morgan