Opensource

In practice, that would require buy-in from the apartment/house association board, since the average resident would be unlikely to care about whether or not the software was open source or owned by the association. Cost would likely be a more important metric for most members, and here a company that serviced multiple associations would likely have an edge, especially since they could also provide general support to the end-users.

If it did get approved by the associations members, then the board would then likely have to hire a third party do carry out the actual development. If you're (very!) lucky, then one or more members might be willing to do it cheaper than a third party, but that would likely only last for however long they lived in one of the apartments or houses.

I would put this scenario down as possible in theory, but very unlikely to work out in practice. The vast majority of such associations would go with an existing (closed-source) SAS provider, since that would be a lot less work and since it would survive the constant turnover in such an association.

I honestly have an even harder time seeing how it would work out for OSS in general, since most software does not come with an existing organization, nor a community that is as directly invested as residents in an associations. For most projects, the work involved in setting up and managing such an association would greatly exceed the work involved in developing the software itself, which, similarly to the above, most of the users would not be able to contribute to

EDIT: A more plausible scenario for an house/apartment association, would be somebody setting up a company structured as a co-op and then recruiting multiple associations as co-owners/customers. Is that what you had in mind? Though that of course requires that somebody has both the funds and the interest to get it off the ground, which is unlikely to be an existing association