Different from co-ops, but a lot of small funds (micro-VCs, etc.) have this kind of structure to help their portfolio companies - I actually interviewed at one earlier this summer. There are also similar places like Betaworks (https://betaworks.com). A small few operate as a true collective, but there aren't many.

This article I read recently talks a bit about some of these less-traditional setups: https://www.instapaper.com/read/1341389477