From the UK-based open monograph project COPIM:
Available on Github at https://github.com/BirkbeckCTP/otf-signup, features of the system include order tracking, billing management, notification of new sign ups, and access control for backlist packages of books.
The open source code—developed for the CEU Press initiative to use back-catalogue access membership to fund current OA publishing—should be adaptable to any consortiable funding model. Can’t wait to dive in.