At the RMLL 2018 a very interesting m association management software had been presented, very similar to what have been proposed by @felix . Still french only:
The developer of garradin says that it has very poor support for i18n and recommends http://galette.eu to international users.
Tougher, and strong is also erpnext, but probably not the slimmest tool around, but it seems that to do stuff right and proper. Would be awesome to have some service-people to do support and teachings regarding that. Has a agriculture module as well, btw.
The fairkom guys are using it (at least) for their shop and might share some experiences.