MemberLeap - Member Leap offers membership management, website content management, billing, event registration, and several cloud-based applications.
API List - A collective list of APIs. Build something.
WildApricot - WildApricot is a powerful cloud software to help you automate and simplify membership tasks.
Abstract APIs - Simple, powerful APIs for everyday dev tasks
AMO - AMO allows to manage membership information in one place with an integrated website builder, manage communication and engagement.
Phantombuster - A marketplace of simple to use no-code APIs