OBM is a groupware, email, LDAP, CRM, and project management application. It is mainly used as an Exchange or Notes/Domino groupware and mail server replacement, as an LDAP directory, as a contact and customer database, as a project management tool, or as any combination of these functions. It provides groupware (calendars, contacts, and tasks) connectors for Outlook, Thunderbird/Lightning, and mobile devices. It supports internationalization and themes. It is highly scalable, and is used by sites from five to many thousands of users.
OBM is being developed by Linagora and licensed under the Affero GPL 3, you can find more information about OBM and how to get started with development at obm.org