Sadly I don’t think something like this does exist
Although it is obviously something that should!
I know a while back (April 2016) @siborkin was trying to make something (the latest iteration of something) like this happen called ‘Our Society’ (which support from people at Outlandish so perhaps @harry or simon can tell us more?) , but sadly I don’t think it went anywhere?
Simon: am I OK to post the 18pp PDF you sent me about the idea here?
For my own part, it’s been obvious to me we need to create something like this since at least Feb 2011 when I posted this: https://uniteddiversity.coop/crowdfunding-cooperative/
And I believe that had Emily Mackay who started Microgenius (originally a crowdfunding platform just for community shares in energy co-ops, hence the name, a reference to micro generation), handed the platform over to myself instead of selling it to Co-ops UK/ Community Shares Unit that it would’ve since turned into something much like what I outlined above (instead of closing down and just being replaced by this listing https://communityshares.org.uk/share-offers/microgenius - which the old url http://www.microgenius.org.uk/ doesn’t even redirect to).
These days it seems most Community Shares done online are done via Crowdfunder (in partnership with Dave Boyle of https://communityshares.co.uk/ ).
Somewhat frustratingly, the platform that became Crowdfunder (originally Peoplefund.it) was funded by Nesta with the stipulation that it be an open source platform, but in the end only a single undocumented snap shot of the code was ever published, and now even that has disappeared too (it was at https://github.com/keofilms/Peoplefund.it ).
I had a great meeting with someone involved with PeopleFund.it before they even built the platform and strongly suggested it be a platform for doing community shares as at the time no one was doing it, but alas they didn’t (until many years later)
(at the time I was also arguing for it to be made in Drupal(!) but they hand coded it in PHP instead - there is a funny thread where they told me their developers didn’t want to use Drupal as they like PHP and I informed them that Drupal is PHP)