As far as I know, there is no alternative. To develop and deploy an app just track the documentation and look at the other app repos. https://doc.owncloud.org/server/latest/developer_manual/app/introduction.html. If you want to put your app to marketplace, there is a section for code signing and publishing also.
furthermore i think it could make sense to update to the latest available version 10.0.9 as 9.1 and 9.0 are already unsupported. This makes sure that you’re developing an app which is based and working on a supported version of ownCloud.