Developer Documentation — Everything you need to know for customizing, extending and debugging CiviCRM.
Community 'notepad' wiki— ARCHIVE of notes for collaborative planning, requirements, specifications, notes from sprints and anything else. Since 2017, CiviCRM has been moving to a working-groups team structure and using Gitlab on lab.civicrm.org to structure group-specific collaboration, as well as using Mattermost on chat.civicrm.org for discussions. Not sure where to start from? Ask on the chat! either in the "town-square" or in one of the group-specific channels. (more information on how CiviCRM uses Gitlab)
