Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
PowerSchool - PowerSchool provides a K-12 education technology platform for operations, classroom, student growth, and family engagement.
Roundcube - Web-based IMAP email client
Clever - syncing between education applications for K-12 schools
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
Claroline - Claroline is a collaborative eLearning and eWorking platform.